I would love to see metric fasteners on all automobiles go to either even or odd numbers. The number one reason I hate working on metric cars is they use all the damn sizes and I cannot eyeball them. Why they feel the need to build a car using 7,8,10,11,12,13,14,15,and 18mm is ridiculous. At least with SAE I can tell the sizes by looking at them because they are 1/16" increments.
Metric VS Standard fasteners
- Thread starter Matt018
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AZ_Catskinner
Well-known member
Notice the condescension with which some of the metric system fans speak? I have made it abundantly clear that I don't see any legitimate superiority in either system, again though I do concede that metric is much simpler for people unable to comprehend fractional measurement. I can do dimensional work in either system without any problems, just because I'm willing to do the damned work. We did it just fine for a whole lot of years without worrying about how much better the other system was, didn't we? Last time I looked, my Imperial micrometers and indicators were every bit as accurate as their metric counterparts. I don't think a metric tape measure is any more accurate than it's Imperial counterpart either. If you really want to get technical, Imperial measurement is simpler when decimalized, based on the fact that studies have shown the naked eye can discern .01" which translates to .26mm. In order to transfer that to a ruler, you'd have to fractionalize the millimeter which pretty much destroys the entire concept of the metric system.
"The people making the decisions" (typically engineers) and their computers rarely get anything within an inch of what it's supposed to be much less a millimeter, leaving the "wrench turners" to clean up their mess. Regardless of what measuring system is used, they still make shims for a reason, don't they?
"The people making the decisions" are also the ones who never bother to compensate for ANYTHING in their designs, making us dumb "wrench turners" do the work that they failed to do in the field rather than in a nice air conditioned office.
If you like metric, great. I'm glad you believe in it, but there's no need to be an *** about it. Everyone has their reasons for preferring one system over the other, and that should be enough.
No, my predecessors determined it was a bit too inconsistent and a bit too much work so they got together and created a consistent set of units and measurements that lent themselves to easy calculation and definition.
This was all done by the middle of the last century by Science: it has taken some industries longer to catch on than others. The higher-tech, higher value industries were first. Furniture manufacturers will probably be last.
Again, go ahead and try to add a dozen fractional measurements together without a rounding error in a computer. It certainly can be done, but it isn't trivial to always do it right and it was a lot bigger problem in 1970.
Yes, I suppose we did just fine without computers, without CAD, etc.
I don't know how old you are: it's possible you don't know why the SI units are the basis for everything in the 21st century. It has zero to do with trivial stuff like rulers. You can make and use whatever sort of ruler with whatever units you want. You can even write fractions of centimeters if you care: some of my metric rulers are marked this way. It's a useful human interpretation.
We have SI units and powers of 10 because they make calculation and collaboration easier, not because they are inherently useful at human scales. Stuff on human scales hasn't been particularly interesting to science for a hundred years.
First of all, the people who made these decisions were not engineers. I went to engineering school in the 2000's and had a prof or two that were still being dragged kicking and screaming into SI units. Engineers are the wrench turners of science. They are not the big picture decision makers.
Accuracy in engineering is economics. The computer I'm typing this on has ~1 billion transistors crammed into a ~centimeter squared of silicon. Intel made a design error on a nanometer scale recently that cost ~1 billion dollars to correct. It's hard to imagine a six inch error in a building or bridge that could cost a tenth that. I get that it must be infuriating to deal with.
Of course. That has nothing to do with a system of units. Metric isn't about being more precise. Precision of measurement is a technical challenge that can be defined in whatever units you like.
CHRIS LUCKYMAN
Banned
Catfight!
Ironically, perhaps, there are several common standards for metric fasteners on cars.
I prefer JIS:
http://www.engineeringtoolbox.com/metric-bolt-head-wrench-size-d_1458.html
8,10,12,14,17,19 will take apart 90% of a Japanese car, bike, jetski, etc. Plus the flanged nuts and bolts are easy to start, easy to handle, just nice. I think I only found one 17 on my last jetski overhaul: everything else was bolted on with one of the first four.
If flanged JIS hardware didn't cost so much at retail, I'd use it for all my projects. Until then it's by the pound USS from Tractor Supply I guess.
To the wrench turner, it does not make a whole lot of difference, to the engineer it does not make a huge difference other than a being a PITA. It makes a huge difference to scientists, but who cares about them...
Where it makes a huge difference is to international BUSINESS AND international CUSTOMERS.
The people who buy the USA's products (Japan, India, China, Australia, Germany, private corp's, etc) will not buy a device that has SAE fasteners. Especially very expensive machines that they do not, or cannot produce locally.
Even the railroad service industry designs and manufactures in metric because they do business all over the world. (I worked in this industry and we sold $15m+ machines to the Chinese, Indians and others all specified in metric)
Likewise, Boeing cannot purchase very expensive and complicated sub assemblies for their 787 with SAE measurements from worldwide suppliers because one no one could build it, and if they could none of it would fit together.
The metric system is good for our county because other countries are more inclined to buy our products, open local manufacturing plants (BMW Mercedes ect) and in the end create jobs!
It just pisses me off that I need two sets of tools, and that some companies are still using standard, so I need to know how to use it in engineering calculations which *****.
garfunkle24
Well-known member
Seems to me that you've had by far the most condescending attitude in this thread, as if we're all just too dumb to work with fractions:
Nice deflection champ. Also, this may be one of the most asinine pieces of illogical "reasoning" I've ever read:
Here:
http://www.amazon.com/dp/B0013L2YV8/?tag=atomicindus08-20
Lots of them out there, just google for engineers tape measure.
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Moose-LandTran
Well-known member
William Payne
Well-known member
Haha thats funny, I am not going to say any system is better then the other but as one who has grown up metric but because of my hobby has to know imperial. There is alot of user friendlyness to be gained by using the metric system, anyone can count 1 2 3 4 5.
PrecisionTools
Well-known member
Metric for me...its just what I grew up with. I will always feel sorry for that NASA scientist who screwed up that Mars lander thing a few years ago - fried it on re-entry because he did the calculations in the wrong system.
I thought that might be the catalyst for change in the US...but nope! Wonder where that poor ****** is flippin' burgers now?
I thought that might be the catalyst for change in the US...but nope! Wonder where that poor ****** is flippin' burgers now?
I just bougth huge mount of wrenches, but it very hard set up SAE sizes, because I can't say which one is bigger then other.
For exampel 3/4 is very hard way to say 19mm, that is even number, 3/4 is no way near even, not even close, it is like "you/mist it". For me 47/64 could be anything, as 61/64 is "relly/close" to something, but never there and I don't like uneven things.
One thing is sure, on wrench it is much easier to see even number and find it, to compare Inch sizes that usually has very small print of "something-something/what is that?"
10, 11, 12, 13, 14, 15...
could be
10.319, 11,112, 12,303, 13,097, 14,288, 15,081
For exampel 3/4 is very hard way to say 19mm, that is even number, 3/4 is no way near even, not even close, it is like "you/mist it". For me 47/64 could be anything, as 61/64 is "relly/close" to something, but never there and I don't like uneven things.
One thing is sure, on wrench it is much easier to see even number and find it, to compare Inch sizes that usually has very small print of "something-something/what is that?"
10, 11, 12, 13, 14, 15...
could be
10.319, 11,112, 12,303, 13,097, 14,288, 15,081
Basically, this discussion has nothing to do with the actual usability of either system. All that anyone seems concerned about is fastener and wrench sizes, which metric is superior in. Other than that, its a toss up.
again @ skiingman:
why do you keep bringing up rounding error. it doesnt exist. well maybe it does when you think 3/8" is .38 not .375, but thats just because you dont want to bother with more than 2 decimals. No one in the real world does that. and a computer/calculator makes it easier, not more difficult
again @ skiingman:
why do you keep bringing up rounding error. it doesnt exist. well maybe it does when you think 3/8" is .38 not .375, but thats just because you dont want to bother with more than 2 decimals. No one in the real world does that. and a computer/calculator makes it easier, not more difficult
AZ_Catskinner
Well-known member
How many countries turn Caterpillar products away because of the mixed fasteners? How many countries turn away Metso (all SAE fasteners) rock processing equipment? The bigger Komatsu stuff has mixed fasteners too. Even O&K (German manufacturer) starts going to SAE sizes after a certain size range.
Heavy industry still relies on mostly Imperial fasteners. Why? I haven't the foggiest idea. The standard for structural iron is Imperial as well. Good luck finding a metric spud wrench (or erection wrench for those inclined to proper terminology).
Some of you have missed my point entirely that NEITHER system is superior in any way, again other than the point that working with fractions is more difficult to learn than base 10 decimals. No condescension there, just a simple fact.
There is no logic in suggesting that metric fastener sizes are easier to learn than SAE or vice versa. If one was raised on a steady diet of millimeters, then it will be easier to spot a 14mm vs a 15mm. If one was raised on 16ths, then it becomes easier to discern a 9/16" from a 5/8".
Shipfittin
Well-known member
Yeah, I've searched and searched for a good one. Most of the time I find them and think that's what I need until I compare it to an actual regular tape measure and find that the Engineers tape is actually 10ths and 100ths of a foot and not an inch.
I know that Komelon says it's Inch/Engineer but kind of has me nervous to buy it without being able to directly compare because it says 10ths and 100ths. You can clearly see it's .1, .2, .3 and so on and not 1, 2, 3 etc. I have a feeling it's really 10th and 100ths of a foot. I say that because obviously .10 would have no special meaning, as in 10" isn't really anything special. It's 12" that makes 1'. So if it was in 10ths of a foot I would imagine it would just be 1, 2, 3 etc. and not .1, .2 and .3.
Stanley 33-272 12-by-1/2-Inch Heavy-Duty Powerlock Decimal Scale Tape Rule with Metal Case
I believe this Stanley is going to be the best out there for what I'm looking for. Notice how it's 1, 2, 3 and not .1, .2, .3 etc.
This is actually a very good example of why the Imperial System, SAE, Fractions, Standard (whatever you call it) can from time to time can be a PIA.
Buckgnarly
Well-known member
I now see why the attempted switch to metric failed in the US...and the Simpson reference posted earlier is now that much more funny.............
Wakefield
Well-known member
When the USA automakers started putting metric fasteners in cars did they go up or down in size? That is did they go up to the next larger mm size or down to the next available mm smaller shank diameter compared to the old SAE one that was being replaced? The thread pitches seem to be a little different-did they choose a better pitch or a worse one? Did the fasteners get stronger or weaker,especially for cylinder head bolts/studs,connecting rod bolts/main bearing cap bolts/studs? Stronger's better?
Within the SAE system they had course or fine-wonder which of those was better in various situations? Did the metric fasteners they chose limit the ability to use the best thread pitch? Were there other thread pitches available in metric stuff that the automakers rejected?
Within the SAE system they had course or fine-wonder which of those was better in various situations? Did the metric fasteners they chose limit the ability to use the best thread pitch? Were there other thread pitches available in metric stuff that the automakers rejected?
BrokewrenchLS1
Well-known member
And you keep flat-out saying that people who prefer to work with a more simple measurement system simply aren't as intelligent as those who work with a fractional measurement system.
Are mechanics stupid because they use air tools instead of hand ratchets? Are painters stupid for using spray guns instead of paint brushes? Are engineers stupid for using CAD instead of hand-drafting everything?
Of course not. Using a more simple measurement system is based on easy logic - it's easier to use, it's easier to learn, has a high degree of precision, scales from one unit to another very easily (mm to km, for example), and is in use all over the world.
The raw basis for the metric system may be as arbitrary as the imperial system (although we could really attribute that to any system of measurement, be it length, temperature, etc) - the length of 1mm is arbitrary. But that's the only arbitrary relation associated with the metric system - all other numbers are based on a logical decimal point change from that initial measurement. Imperial, on the other hand, is arbitrary across the whole spectrum - 12 inches in a foot, 3 feet to a yard, 5280 feet to a mile, etc.
I grew up useing Standard sizes. If I see a standard size I can tell right away, If I cannot tell what size it is I know it's metric. Everything these days is metric. It was a real PIA when I was growing up because everything was suppose to be converting from standard to metric. Here we are now and there is still standard out there. My Snap On Tools dealer and MATCO dealer don't even carry standard tools on the truck. But what realy burns my A** is using my 3/8" drive ratchet with my 15mm socket. The whole world has converted to metric but the drive tools are still 1/4 3/8 1/2 3/4 1" drive.
BrokewrenchLS1
Well-known member
Fine-thread is typically for machine stuff, as you gain more precision when torquing things down because of the greater number of turns to tighten something, but it has to be used in a hard material because the threads are so shallow - they grip hard material, but they won't bite into soft material.
Coarse-thread works great for softer applications (good example - lag bolts in wood) because they have large threads that bite deeply into the material, and the material conforms around the threads to give a strong hold.
I can't say I've ever seen a coarse-thread bolt or machine screw on an automotive application, but I have seen a lot of failed fine-thread stuff used in soft material. For the automotive industry, since they would primarily use fine-pitch SAE bolts, I don't think the changeover to metric would have affected that too much.
I've never seen a metric lag or wood screw, though...wonder how that works in Europe?
William Payne
Well-known member
The whole world has converted to metric but the drive tools are still 1/4 3/8 1/2 3/4 1" drive.
Its called standardisation (spelling?), why make a socket that will only fit one ratchet when you can make a socket that will fit any ratchet made by any brand of the specified size. If you want your drive sizes in metric then start calling them, 6.35 9.525 12.7 19.05 25.4
shampoop
Well-known member
There are only 2 good things about the SAE system.
1. Less sizes overall means less tools needed which means money in your pocket.
2. One thousandth of an inch by pure luck just happens to be a very useful size.
Everything else, metric is better.
1. Less sizes overall means less tools needed which means money in your pocket.
2. One thousandth of an inch by pure luck just happens to be a very useful size.
Everything else, metric is better.
AZ_Catskinner
Well-known member
I really don't know where in the hell you are getting that from. I am saying plainly and simply that base 10 decimals are exponentially simpler than fractions. This is what originally led the charge for metrication. Metric was engineered to be a simple system. This is the single true point of superiority for metric. The inch/pound system by nature requires a broader sense of mathematics than does metric based solely on the number of divisors and conversions to switch between various units.
What we miss out on, and so many of the metric cheerleaders over the years have clung to is that we were taught the basics of imperial measurement as young children, and it really isn't that difficult either. A great example of pro-metric hysteria is this quote I took from http://www.metric4us.com/whynot.html
"No, we don't have a perfectly good measuring system! We have a clumsy, entangled, confusing measuring system! And it not only confuses the rest of the world - no, it perplexes Americans themselves!
If you go to buy carpeting, and you need 100 square feet, the carpet costs $10 per square yard, could you, even given these simple numbers, ever figure out how much you'll pay? Which is more, 2 quarts, 5 pints or 36 fl oz? How many pints are in a gallon? How many pounds are 200 ounces? Which drill is the larger - the 13/64, the 1/4 or the 5/32? Two cities on a map are 10 inches apart - what is their real world distance?"
So the assumption is that Americans are complete idiots, and that we cannot figure out these basic questions. How big of a pain will it be to get the dude at the carpet store to do the conversion of your house's actual dimensions to metric? Special props also go to the genius who decided that map scales are only possible in metric notation.
Neither system is legitimately superior, only different.
4Tigers
Well-known member
There is another good thing about SAE it usually is attached to something old and American!
Think old cars
Think old cars
jvitez
Well-known member
Another good thing: it allows us to buy 2 sets of tools. More toys!
BrokewrenchLS1
Well-known member
No idea at all where I would have gotten the fact that you're being condescending to anyone who prefers the metric system over imperial...if they like metric, they must be too stupid to understand fractions, right?
Gonna shoot off a quick email to all the Nobel-winning scientists in the world who use metric every day, and prefer it over imperial.
Imperial is not superior, in any way whatsoever, over metric. They're not equal - metric is better. It is more precise, it doesn't require asinine format changes (since, to attain the same precision with fractions, you have to convert to decimals), doesn't require asinine scale changes (one single scale, rather than 1/128ths and 1/32nds and 1/8ths), and the base unit the metric measurement system is based on - the meter - isn't arbitrary like every single form of length and distance measurement in the imperial system.
And in the quote you provided, it's not even attempting to say Americans are idiots - it's simply pointing out the confusing, inane, hard-to-calculate imperial system is archaic and slow compared to the metric system. If I have to add 1km, 1.3m, and 37cm, or 1.4 miles, 42.4 feet, 7 9/16th inches, and 13/32nds together - which system is easier, faster, and more efficient? It has nothing to do with how smart or stupid someone is - it has to do with how efficient the system is, and how easy it is to routinely add varying measurements up. The imperial system isn't bad, but the metric system is better.
You completely missed the analogy I made about equating preferring an easier system to a harder system having nothing at all to do with being stupid for liking the easier system more. Is a mechanic stupid because he prefers the easy way - air tools - over the hard way - hand tools? Your argument is synonymous to claiming that any mechanic that prefers air tools over hand tools must simply be stupid. And assuming people who like the metric system over the imperial system are simply incapable of doing fractional math is beyond asinine, it's insulting.
If you don't see how the metric system isn't superior because of that, there's not much anyone else can say.
Heavy Metal Doctor
Well-known member
I thought this was about fasteners, specificly......
Let the rant begin:
I don't care about MPH / KPH on the road signs...lets talk fasteners.....
Yeah, the metric system makes sense in all those points pointed out by its supporters...easier engineering / design stuff and all that...
Standard is just as easy to work with as long as you are not a *******.... both true....great.....that does nothing for actually workin on ****.....
Working on equipment that is mainly built with SAE - weldments / structures all assembled with it...things like pivot pins for hydraulic cylinders are SAE....Then all sorts of components from all sources are put into it to make it work as intended. These parts can be either SAE or Metric depending on the MFR -- Eaton pumps are metric while the Vickers pump right next to it is SAE.....you get the idea where I'm going with this.....in my case its about 70/30 split with SAE still being more common.
This leads to my only real problem with SAE / Metric hardware -- too many other equipment "techs" I have to clean up after can't seem to tell which is which and I often find metric bolts jammed in standard holes....For some reason I don't recall ever seeing the reverse, though....when I hired and guy who'd only previously worked on cars, he tried to use metric tools for everything...with some mixxed results (wasn't the single reason for his downfall, but it helped).....
It's all about education - when you are taught the right way (AND you fricken learn!) - doesn't mater which sytem is more prevalent then neither one is a problem to deal with......either type of fasteners will be "visually learned" when working with them all the time - work on it long enough and you instinctually "know" if it's a 3/8" bolt that takes a 9/16 wrench or it's metric that take 12mm or whatever.....I can't count the number of time I had to explian to other techs how to figure out what size hardware is, (and even hydraulic components / hose connections), simply by the wrench that fits on it.....I know for the most part thay don't see it as often as I do, but some of them are "repeat offenders" and just plain dumb....
Rant over.....
Let the rant begin:
I don't care about MPH / KPH on the road signs...lets talk fasteners.....
Yeah, the metric system makes sense in all those points pointed out by its supporters...easier engineering / design stuff and all that...
Standard is just as easy to work with as long as you are not a *******.... both true....great.....that does nothing for actually workin on ****.....
Working on equipment that is mainly built with SAE - weldments / structures all assembled with it...things like pivot pins for hydraulic cylinders are SAE....Then all sorts of components from all sources are put into it to make it work as intended. These parts can be either SAE or Metric depending on the MFR -- Eaton pumps are metric while the Vickers pump right next to it is SAE.....you get the idea where I'm going with this.....in my case its about 70/30 split with SAE still being more common.
This leads to my only real problem with SAE / Metric hardware -- too many other equipment "techs" I have to clean up after can't seem to tell which is which and I often find metric bolts jammed in standard holes....For some reason I don't recall ever seeing the reverse, though....when I hired and guy who'd only previously worked on cars, he tried to use metric tools for everything...with some mixxed results (wasn't the single reason for his downfall, but it helped).....
It's all about education - when you are taught the right way (AND you fricken learn!) - doesn't mater which sytem is more prevalent then neither one is a problem to deal with......either type of fasteners will be "visually learned" when working with them all the time - work on it long enough and you instinctually "know" if it's a 3/8" bolt that takes a 9/16 wrench or it's metric that take 12mm or whatever.....I can't count the number of time I had to explian to other techs how to figure out what size hardware is, (and even hydraulic components / hose connections), simply by the wrench that fits on it.....I know for the most part thay don't see it as often as I do, but some of them are "repeat offenders" and just plain dumb....
Rant over.....
AZ_Catskinner
Well-known member
So by your own admission metric is a simpler system that requires considerably less mathematical ability? If you do a modicum of research, you'll find that one of the big reasons behind the push for metrication was that it could be picked up by just about anyone with very little in the way of formal instruction or educational background.
I've pointed out multiple times that NEITHER SYSTEM IS SUPERIOR. They both have their faults, and that's just the way it is.
I really would like to know how metric can possibly be "more precise". As I said before, my regular old micrometers work just as well as the metric ones (you know, so I can decimal down a millimeter just the same as I do with an inch).
If you want to talk about insulting, it's your attempts to make a simple point into a big slam against the proponents of a different arbitrary measurement system than the arbitrary measurement system I use. It is especially insulting when said point is one of the major drivers behind the metric movement.
So let's get this straight, metric advocates are apparently offended by their own rationale. Doesn't that seem a little odd to you? Especially when you keep parroting exactly what I keep saying - METRIC IS EASIER.
I admit, I went to school when metric was still a 30 minute conversation once a year.
I've pointed out multiple times that NEITHER SYSTEM IS SUPERIOR. They both have their faults, and that's just the way it is.
I really would like to know how metric can possibly be "more precise". As I said before, my regular old micrometers work just as well as the metric ones (you know, so I can decimal down a millimeter just the same as I do with an inch).
If you want to talk about insulting, it's your attempts to make a simple point into a big slam against the proponents of a different arbitrary measurement system than the arbitrary measurement system I use. It is especially insulting when said point is one of the major drivers behind the metric movement.
So let's get this straight, metric advocates are apparently offended by their own rationale. Doesn't that seem a little odd to you? Especially when you keep parroting exactly what I keep saying - METRIC IS EASIER.
I admit, I went to school when metric was still a 30 minute conversation once a year.
Do you not see that these two statement are mutually exclusive?
garfunkle24
Well-known member
You've admitted metric being simpler and hence, all else being equal, better. What single advantage does the imperial system have?
This is not a question of whether or not people have the mathematical ability to calculate fractions, it's a question of whether or not it's economical, efficient and logical for them to do so.
One system has clear advantages, which is why it has been adopted pretty much every where it matters. You don't hear much about Intel developing a new "12 nano feet" manufacturing process or people describing the focal point of a laser in "nano yards" do you?
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AZ_Catskinner
Well-known member
Not necessarily so - neither is superior to the other in functionality. Any difference in usefulness is purely subjective. There's nothing that one system can do that the other cannot do with equal ability. As for user-friendliness, both systems have their respective niches where they excel, so why not accept both?
Metric is easier to learn, seeing as everything is based in divisions of ten, and there are fewer units to remember. Imperial is considerably more difficult to learn, and conversions DO take more work.
garfunkle24
Well-known member
You have two things that perform the same function. Thing A is easier to use than thing B. Other factors equal, thing A is therefore superior to thing B. QED. So far you've provided no reason that other factors are not equal.
And that, sir, is the ENTIRE POINT, the raison d'être of the metric system. And it's an enormous point....
And that, sir, is the ENTIRE POINT, the raison d'être of the metric system. And it's an enormous point....
...and I'd like to add that I say the above as someone who grew up with Imperial/fractional/whatever you'd like to call it, as someone who can look at a fractional bolt head and eyeball with ease what size it is, who works on vehicles that are almost exclusively fractional, and who only recently bought a complete set of metric sockets (even though I rarely use them). And I see the elegance and simple superiority of metric.
AZ_Catskinner
Well-known member
Ever tried reading a metric grade stake? Metric and dirt work don't sync up well. The old tried and true "tenth" (1.2 inches) is still the standard for a reason. Centimeters aren't big enough, Meters are too big. Even Decimeters would have to be fractionalized to get the same degree of accuracy.
Scientists like metric for the exponential range in large and small sizes, but metric does lack somewhat in the "middle of the road" sizes.
I personally don't think that Intel laser developments "matter" nearly as much as things like decent roads. See? It's all subjective, there's no need to cheerlead for either system.
garfunkle24
Well-known member
I give up. You're dragging me down to your level. Also: The world is not flat and the sun does not revolve around it.
AZ_Catskinner
Well-known member
So what you are saying is that you have no effective counterpoint?
Your signature says it all - a belief that ideology somehow equates to intellectual superiority pretty much says it all. The content of the story it links to borders on hysterical. All this "study" is is a fluff piece written by permanent college students who don't want to get a real job in order to give themselves an inflated ego based on statistics that could be easily manipulated by a toddler. It's not hard to see right through imagined superiority.
garfunkle24
Well-known member
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SAE sizes push you out to six significant figures before any math at all. 5/64 is a drill I have in my toolbox. A few calculations on a 8 figure calculator and you start losing data. You can't calculate the simple volume of a 5/64th hole on a four function calculator without rounding error. Not without an accompanying sheet of paper anyways.
Small metric screws and drills get by with only two significant figures. This gives you much more room for math before error...and smaller errors when you do round. Also easier to calculate by hand, leading to less human error.
I don't have maple on this netbook to show this graphically. If you want me to walk through an example please ask.
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