Metric vs SAE. Pretty crazy how many sizes overlap.
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BlitzcrankJapan
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Anything 0.0x should not be considered exchangeable. Only 0.00x.
With anything under 22mm it's probably better to use the appropriate tools. For larger stuff the measures are close enough so that it should not be a huge issue if you mix them.
To me here in Europe, what's more interesting is that 3/8" is basically a 9.5mm wrench, and 1/2" is a 12.7mm wrench. Can come in useful for stripped M6 (10mm) and M8 (13mm) screws. Would be cool to have a 16.5mm and an 18.5mm wrench too.
To me here in Europe, what's more interesting is that 3/8" is basically a 9.5mm wrench, and 1/2" is a 12.7mm wrench. Can come in useful for stripped M6 (10mm) and M8 (13mm) screws. Would be cool to have a 16.5mm and an 18.5mm wrench too.
I just mentioned this in another thread. While I find metric easier to use overall, I like how SAE seems to have better spacing between sizes in the range of fasteners we often use in cars etc. Between 5/16th and 5/8th you cover roughly the same range of faster sizes as 8mm to 16mm. However, you would typically only need 6 wrench sizes. That same metric range is 9 wrenches and includes sizes that are largely redundant (9, 11mm) as well as sizes where it seems mfrs can't decide which to use (12 and 14mm vs 13mm). So if I'm working on a Japanese car I could skip 9, 11, 13 and 15mm but if the thing came out of Europe I might skip 12 and 14 while using 13 and 15 quite a bit. I will never use 10mm since it's used by both and thus the socket is always lost. The typically 1/16th" steps work out to about 1.5mm per step which seems like a more useful jump when you are in that 10-16mm size range.
ihateminimumwage
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I've definitely run into quite a few fittings where 1/2 wouldn't fit on the 13mm head and 14mm wouldn't fit on a 9/16" head, but have also used 11/16" on a 17mm in a pinch with no issue.
All true, however if everyone used imperial there'd bound to be in-between sizes too.
Sometimes, it's not about making it easier for the mechanic, but quite the opposite. And for good reason. Like, you don't want the mechanic to remove the oil sump when doing a simple oil change, so sometimes using unusual sizes can prevent such mishaps.
Why do the Japanese use different heads than the Europeans, and why are those different to the ISO sizes? Many explanations and calculations and considerations, but a big part is tradition - and that is also why SAE sizes still exist in the US. However at least with a metric set you can practically remove everything and the sizes make sense. To me as an European, the fractions are so ridiculously foreign and I don't want to bother to learn them - I sometimes even measure the screw head with a caliper in milimeters and then go measure through all my imperial wrenches to find the right one.
I really admire that people can use fractions when reading off of a caliper or a tape measure.
kaymccampbell
Well-known member
I can sight measure, no tape or caliper, when picking imperial wrenches for imperial fasteners. Metric, it's a 2 or 3 wrench grab to get it right. That half millimeter means a lot.
cherrybomb
Well-known member
This chart makes sense as a home gamer and living in the rust belt.Another part of the equation is the tolerance the manufacturer of the fastener used.Sometimes you have to just use what fits the best.This chart helps substitute in certain situations
One issue with looking at it this way is that a certain linear gap means very different things at the top vs bottom of the chart.
I made this one to also account for the angular play: https://www.garagejournal.com/forum...nch-sae-tool-interchangeability-chart.510030/
I made this one to also account for the angular play: https://www.garagejournal.com/forum...nch-sae-tool-interchangeability-chart.510030/
mike93lx
ALLIANCE MEMBER
That's what she said
I bet that's all just experience. Imagine the German GJ-equivalent has people saying the same about our stupid fractions-of-a-banana junk
RoninB4
Well-known member
There is some overlap between inch/metric, sometime makes a difference and sometimes not so much. I've worked with both systems most of my life but use decimal inch notation in my head. I'll gauge the fastener head (or socket head) by eyesight and estimate how much torque is applied. If it's not much either inch or metric (if close enough) will do. If there's a chance of deforming the head/socket I'll measure with a caliper for over/undersize and select the best size I have. There are oddball wrench sizes in both system (19/32", 5.5mm for example) and the old ignition wrench sizes that seem particular to some equipment.
Your comment about fractions reminded me of an interesting Youtube math program I watched. The person was basically making the argument that it's unfortunate that we choose a base 10 number system. That is we count to 9 then at 10 we switch to two digits. He suggested that some of the earlier number systems that were based 12 would have been better.
The argument was something to the effect that base 10 doesn't work well with factions and dividing things into even intervals of 1/2, 1/3 and 1/4 of a whole is actually a very common thing for people to do. 1/2 of 10 is easy, 5 But 1/3 of 10 is an infinite series (3.3333... ). 1/4 of 10 is 2.5 so now you have a fractional number. 1/5 of 10 is good (2) but 1/6 of 10 is well useless.
Compare that to base 12. 1/2 of 12 is 6. 1/3 of 12 is 4. 1/4 of 12 is 3. So the most common fractions all work nicely, especially 1/3 which is inherently problematic in a base 10 system. If, way back in time, we had decided on a base 12 number system then perhaps metric would be happy to use fractions as well. As someone who works in both unit systems I often think in both fractional and decimal terms. I also used to be decent at recognizing decimal inches that were based on 1/8ths or 1/16ths of an inch.
That's an interesting thought. But if we take 10 cm, it's still easy to imagine half or a quarter or a third of it. The problem I have with the fractional system is the more strange stuff. Like, I really cannot imagine 5/32, 3/16, 7/32, 9/32, 5/16, 3/8 etc...
I'm not used to it. For me to imagine 3/8 (which I assume it's a common wrench size kind of like 10mm), I have to do math in my head. It's obviously less than one half, and it's basically a "quarter plus a half of a quarter".
If we go back to 10cm, 3/8ths out of that is 3.75cm. To me the decimal is just way easier to imagine. It's a little less than 4cm. You could also say it's 3cm plus 3 quarters of a cm.
I expect I'm over omplicating it cause I'm not used to such a system.
For mental math, a base system of 12 would be easier to handle, but I don't think it would make daily conversation any easier. Besides the fact we all have calculators in out pockets, you can also just sit down and write the calculation and then I think a base system of 10 is a lot easier to use for math in that way.
It's of course way too late to change to base 12 now but in my design work I frequently want something divided into 3rds or quarters for functional reasons. It would be nice if the math system were such that dividing by 2, 3 or 4 always produced a clean new number the way dividing by 2 and 10 do with our current number system (metric or decimal inch).
nadogail
Well-known member
Our measuring system is similar to our language, in that it is made up of things borrowed from a lot of different places; we seem to be stuck in our ways and too stubborn to change.
We have refused to change to Metric, probably because it was not invented here. We are who and what we are, and we will probably stay that way.
Who needs a logically based measuring system based on scientific principals? We are not the only country not using Metric, to the best of my knowledge, Liberia is using the same measuring system as the United States.
We have refused to change to Metric, probably because it was not invented here. We are who and what we are, and we will probably stay that way.
Who needs a logically based measuring system based on scientific principals? We are not the only country not using Metric, to the best of my knowledge, Liberia is using the same measuring system as the United States.
American Locomotive
Well-known member
As the fastener gets larger, the allowable tolerance becomes larger. On a 24mm fastener, "0.0x" is just fine.
Here's my own experience for substitutions:
5/16 - 8mm: Seem to universally interchangeable. Never had an issue subbing one for the other.
1/2" - 13mm: 1/2" sometimes works on rusty 13mm bolts, but is often too tight. 6 point 13mm always seems to work fine on 1/2" bolts. 12 point can be iffy if bolt is rusty.
9/16 - 14mm: 9/16" always seems to work on 14mm bolts. 14mm sometimes a bit snug on 9/16.
3/4" - 19mm: Universally interchangeable
I find that on the big sizes (1"+), you can get pretty sloppy on the fits and still have it work.
Inches weren't invented here either. I think the biggest problem is that for a long time it was easy for US companies to be isolated and thus stick to what they knew vs what others were using. That and let's be honest, is not easy to change. It likely to the car companies 2-3 decades to convert. Now consider sectors that have even longer turn over times. Aircraft designed in the 50s are still flying today. Imagine the impact to home building if dimensional lumber was changed to metric standards. Does the standard 16" spacing between studs become 40cm or 50? Can I still use 15" insulation batts in a 40cm on center ceiling? I'm a big fan of converting but it's also a huge job and, unlike a decision to switch from right hand to left hand drive, this would take decades to do and likely have lingering effects for a century or more.
As someone who has dealt with base 16 (hexadecimal) enough in the computer world, I will argue that base 10 is SOOO much easier to deal with. Hell, I'd take binary (base 2) over base 16. Yes, in theory you can do A + A = 14 easily enough in your head, but ughhh
I'm assuming if we used base 12 or even base 16 it would be as natural to us as using base 10. We are used to it so we don't have to think about it.
BDT/NWMN
Well-known member
A few years back, I came across fasteners on a 1929 Model A Ford where I used metric wrenches because some of My "common size, current day" SAE wrenches didn't properly fit. I had to chuckle when thinking about an old, ancient socket set My Uncle gave Me about 65 years ago. The entire set is stepped in 1/32" instead of the common current day 1/16". Might have to go on a relic wrench hunting spree so I also have the "proper" size wrenches to work on that Model A. 
Stelzer
Well-known member
Rounded fasteners not withstanding
HannibalLecter
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The obvious number for fractions meaning that can get divided by many numbers and give whole numbers is 60, not 12 .
Either way trying to do calculations and simplifications of forces with a base other than 10, good luck.
1.2345x12^3 - 5.67x12^6 , try to simplify and divide 1.2345 with 12^3 in your head, see?
And then try to do 12^6 .
Maybe I am missing something but it gets frustrating pretty quickly
Let's leave math to those who do actual calculations, not the ones that just get inconvenienced because 10 cant be divided by three and give a whole number
Either way trying to do calculations and simplifications of forces with a base other than 10, good luck.
1.2345x12^3 - 5.67x12^6 , try to simplify and divide 1.2345 with 12^3 in your head, see?
And then try to do 12^6 .
Maybe I am missing something but it gets frustrating pretty quickly
Let's leave math to those who do actual calculations, not the ones that just get inconvenienced because 10 cant be divided by three and give a whole number
vavet
Well-known member
So how would that work? Would the numbers ten and eleven get new characters to represent their new identity? 11 would still be 6+5, but it would be a single character instead of two characters?
22 would then be represented by a 1 and new character?
Its an interesting idea, but I suspect it falls into the “grass is always greener” phenomenon And would have its own weaknesses we would discover after we tried to use it for a while.
maybe when we set up the Mars colony, we can try that system along with all metric. if this is something that should gain traction you need someone like Elon Musk who just ignores people who say it can’t be done and does it anyway….either that or Oprah. I’m convinced that lady could do just about anything with the support of her followers.
the job I just left was a manufacturer of bowling equipment, it was all Inch hardware…except for the things that were not. Design engineers claimed it could not be converted to metric because some of the oddball, custom fasteners we used would be impossible or very expensive to source. We shipped equipment all over the world along with a tool kit, so I guess those customers figured it out. Sometimes we’d source an assembly to China and they would build it with metric hardware instead of having us ship them inch hardware….so then you would have a 6mm nut and bolt in an assembly that is held in the machine by 5/16 bolts. It’s a horrible thing to do to a mechanic.
Basically yes. We already do this with hexadecimal math. In hex the number go 0 1 2 3 4 5 6 7 8 9 A B C D E F. So 9+2=B. Hex is useful for people working with 8 bit numbers since an 8 digit binary number can be expressed as 2 hexadecimal numbers. FF=255=11111111 in binary. F0=240=11110000(b). Additionally, each block of 4 binary digits (a 4 bit number) can be expressed as a single hex value (1111=F).
Is base 12 better than base 10? I suspect it generally would be. Almost all math would be just as easy/hard as it is now but we would be used to counting to 12 instead of 10. The only two places I can see a real difference is when signalling a number with your fingers and it might be harder to convert to decimal/hex etc when doing computer work.
It would be hugely easier when dealing with dividing things in thirds or quarters since those would be as easy as dividing by 2 or 5 in our current system.
1. On acceptable fit. I’d argue it’s not a fixed +/- .1mm, more like about +/- 0.5%. So 13mm would be .5118” +/- .0026” (so 1/2” is not close enough). But 30mm is 1.1811” +/- .0059”, so a 1-3/16” (1.1875”) probably close enough, if you have one.
2. Individually the units in the imperial system are good, but they’re not a consistent system. As a system, metric wins. Even ignoring conversion factors of 12, 16, 128, 1760, 5280, etc, how many ounces are in a gallon? How many pounds are in a ton? (Hint - the answer changes based on what you are measuring, and where you are).
3. For fasteners the best system would probably be set up like British Association threads. It’s kind of messed up being a metric thread converted to inches rounded to .001”, but the idea is good. Every size has a factor of 0.9. So instead of 1/16” or 1mm increments, a 1BA is 0.9x the size of a 0BA. And a 2BA is 0.9x the size of 1BA. It makes sense the increments would be larger for larger sizes. But current metric is probably good enough.
2. Individually the units in the imperial system are good, but they’re not a consistent system. As a system, metric wins. Even ignoring conversion factors of 12, 16, 128, 1760, 5280, etc, how many ounces are in a gallon? How many pounds are in a ton? (Hint - the answer changes based on what you are measuring, and where you are).
3. For fasteners the best system would probably be set up like British Association threads. It’s kind of messed up being a metric thread converted to inches rounded to .001”, but the idea is good. Every size has a factor of 0.9. So instead of 1/16” or 1mm increments, a 1BA is 0.9x the size of a 0BA. And a 2BA is 0.9x the size of 1BA. It makes sense the increments would be larger for larger sizes. But current metric is probably good enough.
RalphInCA
Well-known member
Well… They kind of sort of overlap.
Don’t trust the overlap on a stuck or very tight bolt.
“Right tool for the right job“
Don’t trust the overlap on a stuck or very tight bolt.
“Right tool for the right job“
inphx
Well-known member
Thanks for the chart - i am disorganized and don't have socket rails so the chart cheat sheet is now printed when i'm hunting a little smaller or higher...
Also, on the question of fractions -
I work in fractions. I go back and forth fluidly between fraction and decimal inches. People often seem to think 1/2 more readily than 0.5, but struggle with smaller than 1/4 increments. I wonder how much of that is learning vs inherent… for all the fractions we use, people are terrible at them. Years ago A&W miserably failed at marketing a 1/3 pound burger because people thought it was smaller than a 1/4 pound… there’s a marketing lesson in how to craft a message, but also would we be better off just encouraging decimals as more mathematically intuitive?
I work in fractions. I go back and forth fluidly between fraction and decimal inches. People often seem to think 1/2 more readily than 0.5, but struggle with smaller than 1/4 increments. I wonder how much of that is learning vs inherent… for all the fractions we use, people are terrible at them. Years ago A&W miserably failed at marketing a 1/3 pound burger because people thought it was smaller than a 1/4 pound… there’s a marketing lesson in how to craft a message, but also would we be better off just encouraging decimals as more mathematically intuitive?
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chris142
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Im the opposite. I can site measure mm stuff but not sae very well
CHI_Tool&Die
Well-known member
Funnily enough, I was helping my apprentice put together a US General tool cart the other day and we could not figure out what size the nuts were. A 1/2” socket/wrench fit really snug but then so did a 13mm but with some play. I would’ve thought coming from China it would be all metric but maybe it isn’t? I run into this same problem all the time building out die sets at work. The SAE fits really snug and the metric is kinda loose and you just pray that the wrench you go with is going to work. This is why I love SHCS fasteners. No guessing. It fits or it doesn’t.