Metric/std fastener interchangeability

[ckucia]

So I'm sorting through my can of fasteners.

In the past, I've had drawers for standard fasteners, but I never had enough metric ones to justify their own drawers.

Now that it's been a few years and we've been through several cars that were exclusively metric, I have a fair amount of metric fasteners to sort.

I noticed the other night that M6-1.25 bolts fit 1/4-20 nuts and vice versa.

I did the math, and a 1/4-20 works out to a M6.35-1.27. Likewise, a M6-1.25 ends up being .236-20.32.

I assume there's enough slop in the threads, especially in a nut that doesn't have many, that it makes these two sizes appear to fit each others' bolts/nuts.

I also assume that, if I had a decent length threaded bore, that the bolts wouldn't go in the wrong bore, although I don't have anything handy to try that out.

I suppose if the threads aren't too sloppy, I could put a set of calipers on the bolts and sort the two out by OD. Not sure if that would work on the nuts.

Curious if anyone else has come across this, and how you deal with them. Just throw 'em all in the same drawer with both labels and sort it out when you have a deep bore? Get a better set of thread gauges (I usually just use a known-size nut, but obviously that system has broken down)?

Are there any other common fasteners that appear to interchange across both metric and standard?

The only reason I caught this one is I happened to have the metric ones in a pack from the parts store with the M6-1.25 label still on it. Otherwise, I would have just assumed I tossed a standard bolt in the metric bolt bin and set it in the 1/4-20 drawer.

 

[kamesama980]

Not sure without a caliper or long enough threaded hole to see the difference. Usually I take a known bolt and try to lay the unknown threads into it's threads. If they're the same, they go in. all the way and evenly. I sorted out a box of taps quick enough that way. (garage sale find. many, through use or surface rust lost the labels)

That's the stuff mechanics nightmares are made of. I've come across it where someone's mixed them up and boogered the threads. done once, neither fits well. Assuming the bolt doesn't get broken off or threads stripped.

 

[justsam]

There are more to fasteners than the fact that in a few cases there may be a metric and SAE that seem to screw together. There are other angles and tolerances to consider.

I would invest in a good set of thread gauges, and you can use the go/no go gauges for diameter.

There is an excellent book on fasteners, by Carroll Smith.

http://d202m5krfqbpi5.cloudfront.net/books/1328863885l/710357.jpg

 

[Leaflessshadetree]

The common pitch of M6 is 1mm. I'm not sure where you got the M6 x 1.25 fasteners but I would save them for the intended application.

 

[nehog]

...
I noticed the other night that M6-1.25 bolts fit 1/4-20 nuts and vice versa.
...

Uh, no they don't. They are close, and if you have some poorly sized parts you might be able to fit them together, but they don't fit.

 

[4xdog]

Mixing and matching SAE and metric just 'cause they seem to fit sounds like the makings of a nightmare for somebody down the road.

Sounds sorta like the kind of thing my Dad woulda done. He was a Depression-era kid who would re-use all kinds of things to make do that really didn't. His experience was a good object lesson for me and my brother; we learned do use the right tool, and the right fastener, for the job. I'm happy to recycle fasteners and do it all the time. But I do not recommend mixing and matching thread types.

 

[383 240z]

I noticed the other night that M6-1.25 bolts fit 1/4-20 nuts and vice versa.

NO THEY DON'T!! Don't do it they will not come tight, if they do they will not STAY tight. I MIGHT be able to see doing it if your going to bolt a wheel on a push mower but come on good hardware is not expensive. Do it once and do it right.

I know I come off gruff in things like this, I would hate to hear you post how your kid got hurt because an $0.18 nut came off their bike when they went for the brakes as a numb nut blew a stop sign. Keith

 

[ckucia]

Luckily, I don't have so many metric fasteners that this is going to be a huge problem, but I'd prefer to positively identify them.

I didn't even occur to me until the other night that you could mix metric and std bolts and nuts and have them screw onto each other without binding.

Makes me wonder how many of the bolts and nuts in my 1/4-20 drawer are already M6-1.25.

I think some decent thread gauges are probably the best solution. Some of the 1/4-20 fasteners are pretty sloppy - even the ones where I got the bolts and nuts bagged together from Home Depot (not that HD is the pinnacle of quality or anything). I think that if I were using higher-tolerance threads to check the fasteners, it'd be a bit easier to sort them out.

BTW, the M6-1.25 came from the parts store. I specifically bought them for something - most likely is my wife's old (94) Altima. That's the metric vehicle I've done the most work on over the years as it's our oldest, and it's rusty so I tend to have to replace fasteners. Our other metric vehicles aren't as old and I generally only need to replace something if I lose/misplace it.

 

[Milton Shaw]

The auto makers have been mixing metric and SAE for years. SAE for bolts into the block, metric for bolts into anything else. Made it so you had to have both kinds of tools for just about any repair. Now they have gone and done it even better on some of the China stuff that has metric heads but SAE thread and shank. Wish they had never invented one or the other and could standardize on one head and shank standard.

 

[Zeke]

**** hardware that comes with chicom parts to assemble might cross over, but good SAE stuff won't thread onto this junk. I'm pretty sure if you try any Grade 5 or 8 it won't work.

 

[fxgmech]

Please don't mix them up! The SAE bolts will have the radial dashes on the head to ID grade. The metric bolts and most metric nuts will have a numeric grade ID, eg 8.8, 10.9, etc on the head and nut. Or keep them in the original package. Anything not identified and misapplied is going to cause someone much wasted time some day.

 

[ozyborn]

Take metric threads. Retap to SAE. problem solved. I despise metric. Love working on my old cars.

 

[ckucia]

Well, unless I mixed up the bolts, the supposed M6-1.25 bolts have radial grade markings. That would seem to make them SAE.

Is it possible that someone packaged 1/4-20 as M6-1.25?

I was at the parts store tonight - I should have picked up another package just out of curiosity.

 

[Nick Danger]

Take metric threads. Retap to SAE. problem solved. I despise metric. Love working on my old cars.

Why do you despise metric?

I'm guessing that your old cars aren't British sports cars.

 

[ChevyEFI]

A thread pitch guage of any reasonable thread length will show a given thread to be a mis-match, such as 1.25 and -20.

 

[4xdog]

Why do you despise metric?

I'm guessing that your old cars aren't British sports cars.

My 51 year old Triumph doesn't have a metric fastener on it (at least not one I can ever remember). A couple of Whitworth, yes, but metric, no...

But it's only a fastener! I like metric as much as anything else. Life's too short to hold grudges against nuts and bolts.

 

[Thruxton]

My 51 year old Triumph doesn't have a metric fastener on it (at least not one I can ever remember). A couple of Whitworth, yes, but metric, no...

Except for your spark plugs and then there are those BA, and CEI, and BSP (maybe) threads, and prolly a few others...

But it's only a fastener! I like metric as much as anything else. Life's too short to hold grudges against nuts and bolts.

Love it! How true...

 

[4xdog]

Except for your spark plugs ...

Hah! True enough! But aren't they made 14 x 1.25 to an SAE standard?...

 

[Thruxton]

Hah! True enough! But aren't they made 14 x 1.25 to an SAE standard?...

Through simple lack of knowledge, I'm not going to challenge that one...

 

[lynnbilodeau]

Why do you despise metric?

I'm guessing that your old cars aren't British sports cars.

Actually, a lot of the old British stuff is Whittworth thread, isn't it?

 

[Sureshot]

The common pitch of M6 is 1mm. I'm not sure where you got the M6 x 1.25 fasteners but I would save them for the intended application.

Is that not what some suspension components use? I know I had some that were odd.

 

[Nick Danger]

Actually, a lot of the old British stuff is Whittworth thread, isn't it?

I was thinking about Whitworth when I made the comment. Joke fail.

 

[GYPSY400]

How about using a wrench to dictate bolt size?? M6 will probably be a 10mm.. And 1/4" will be 7/16"..
Be careful when you get to M8 and 5/16" tho.. a 13mm wrench is .5mm larger than 1/2" and the diameter of the bolt is the same.. but the thread pitch is different. If you have 5/8" bolts, hopefully you don't have any M16.. lol

Sent from my SGH-I747M using Tapatalk

 

[APEowner]

It's quite possible they were miss bagged. A screw pitch gauge will show you what's what. I don't remember where I got them but I've got a set of inexpensive thread gauges that are discs with marked holes through them and pitch gauges cut into the sides that I really like.

Also, I throw out any bolts that don't have a grade marking.

 

[wornoutoldman]

With the ****** fastener that you find in in most big box and even smaller hardware stores these days I can see why you'd want to recycle fasteners you have on hand. That said, don't mess around with SAE/Metric mis-matches. As previous posters have mentioned, it's just looking for trouble. I would use a thread gauge and run suspect nuts/bolts together by hand to be sure they work/fit correctly in the application. Interchangeabilty? No such thing!

 

[James_B]

Oh the joys of different bolt specifications.

I spent many years working in an industry that used electronic equipment bought from suppliers all over the world, and some of it was still in use 40+ years after it had first been installed.

You couldn't guarantee the kind of nut or bolt you'd encounter until you physically took it out and measured it. It could be Whitworth (including BSW, BSF, and BA), Metric, and SAE (UNC and UNF). After years of experience, many of them you could pick by sight, but you couldn't count on the fact that a previous repairer had refitted a bolt from the correct standard when repairing an item.

Many of the SAE and Whitworth bolts shared thread pitch but the thread profiles were different, so they didn't torque right, but a stuff like BSW 1/2" and SAE 1/2" which had a 1 TPI pitch difference with 12 and 13 TPI respectively were always a problem when somebody had brute forced those two mismatching threads together.

 

[StillKeen]

Definitely keep both sets separate. I've had some that screw on by hand, but if you tighten them up, the threads strip due to limited engagement. Plastic compartment boxes are so cheap these days.

Interesting fact (thanks wikipedia) ''according to the CIA Factbook, one of three countries that has not adopted the International System of Units (SI) metric system as their official system of weights and measures, along with Burma (Myanmar) and Liberia... In 1866, Congress authorized the use of the metric system[3] and supplied each state with a set of standard metric weights and measures. In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metre Convention or the Treaty of the Metre.''

Given the rest of the world use metric, I would say that 'standard' = metric, and imperial = oddball. If the US could stop making imperial fasteners, then I'd need half as many sockets, allen keys, wrenches etc. I'm sure if the US went fully metric, Liberia and Burma would soon follow suit.

 

[LigouriRd]

I noticed this on my first trip to the UK for work. I needed to retrofit a bracket on a couple of pieces of prototype equiptment (that would be destroyed once testing was done) and could not find any "Imperial" fasteners. It took a little effort but M5 fasteners went into the 10-32 tapped holes in the base aluminum parts. A #10 has a nominal dia of 0.190 = 4.8mm and the pitch is 1/32 = 0.79mm close enough for a M5 x 0.8 fastener.

If it were any other situation I would not have mismatched fasteners but the department head was holding my passport hostage in case I did not complete the retrofit...not really but my co-workers joked that he would.

 

[k p]

Take metric threads. Retap to SAE. problem solved. I despise metric. Love working on my old cars.

Right.

Because 3/16", 1/4", 5/16", 3/8", 7/16" is so much simpler than 1,2,3,4,5,6,7,8 etc.

Just like water freezing at 32 is simpler than water freezing at 0.

/sarcasm

 

[spy604]

Right.

Because 3/16", 1/4", 5/16", 3/8", 7/16" is so much simpler than 1,2,3,4,5,6,7,8 etc.

Just like water freezing at 32 is simpler than water freezing at 0.

/sarcasm

And its way easier to remember the drill size for 1/2-13 is 27/64"

 

[ozyborn]

Right.

Because 3/16", 1/4", 5/16", 3/8", 7/16" is so much simpler than 1,2,3,4,5,6,7,8 etc.

Just like water freezing at 32 is simpler than water freezing at 0.

/sarcasm

When you lived you whole life working on older Chevelles and such. SAE is the only way and it is second nature. This is the case where the rest of the world is wrong.. SAE only cars in my garage.

 

[nehog]

And its way easier to remember the drill size for 1/2-13 is 27/64"

And that the drill size for a tapped 6-32 hole is a #36 bit. Unless you want a loose fit, then a #35 works better.

 

[Daniel Dudley]

Next up; Fuel Injection. Is it the new standard, or just modern foolishness ?

 

[JimVonBaden]

I do not have a standard wrench or socket in my kit! I own nothing that uses them.

Jim

 

[NHBandit]

The auto makers have been mixing metric and SAE for years. SAE for bolts into the block, metric for bolts into anything else. Made it so you had to have both kinds of tools for just about any repair. Now they have gone and done it even better on some of the China stuff that has metric heads but SAE thread and shank. Wish they had never invented one or the other and could standardize on one head and shank standard.

This is true and I believe one of the big reasons is to keep the engines standardized so they remain interchangeable. Such as Chevrolet smallblocks. An engine from a 1955 will bolt into a 1990, etc. That being said, it has nothing to do with threading a bolt made to SAE specs into a hole or a nut made to Metric specs or vice versa. That does not work, should NEVER be done, and can potentially cause a dangerous failure. Use the right stuff or send it to someone who's not a ***** (not directed towards you lol).

 

[ChevyEFI]

This is true and I believe one of the big reasons is to keep the engines standardized so they remain interchangeable. Such as Chevrolet smallblocks. An engine from a 1955 will bolt into a 1990, etc. That being said, it has nothing to do with threading a bolt made to SAE specs into a hole or a nut made to Metric specs or vice versa. That does not work, should NEVER be done, and can potentially cause a dangerous failure. Use the right stuff or send it to someone who's not a ***** (not directed towards you lol).

Let us know how the mounts fit the sides of that 1955 block.

 

[NHBandit]

Let us know how the mounts fit the sides of that 1955 block.

Lol.. got me. I stand corrected. But... the 90 block has the threaded holes for the 55 front mounts. Just might or might not have the casting for the mechanical fuel pump fully machined. As for the guy with the 51 Triumph if I remember correctly the threads for the side covers are SAE and everything else is not. Then in the late 60s they started switching over to SAE and you'll find both types of threads for a couple years. By 1970 or so nearly everything was SAE other than head bolts and maybe a couple of other minor things. Yeah I had a part time British bike shop in my garage for awhile and a Triumph or 2...

 

[1/2 Cup]

We have had metric stuff out here for years, along with SAE and Whitworth, I still keep them all separate and do not interchange them at all. I also have a good range of thread gauges which helps however you get to know whats what by sight when you work with them all the time.
I still store them all separately as well.

 

[4xdog]

Lol.. got me. I stand corrected. But... the 90 block has the threaded holes for the 55 front mounts. Just might or might not have the casting for the mechanical fuel pump fully machined. As for the guy with the 51 Triumph if I remember correctly the threads for the side covers are SAE and everything else is not. Then in the late 60s they started switching over to SAE and you'll find both types of threads for a couple years. By 1970 or so nearly everything was SAE other than head bolts and maybe a couple of other minor things. Yeah I had a part time British bike shop in my garage for awhile and a Triumph or 2...

Just to be clear, My Triumph is a 1962, so it's 51 years old. And it's a TR3 (four wheeled).

There are a few Whitworth fasteners (the SU carbs, some of the Smiths stuff), 13/16" spark plugs (with M14 x 1.25 threads into the head), and a whole bunch of SAE.

 

[NHBandit]

Just to be clear, My Triumph is a 1962, so it's 51 years old. And it's a TR3 (four wheeled).

There are a few Whitworth fasteners (the SU carbs, some of the Smiths stuff), 13/16" spark plugs (with M14 x 1.25 threads into the head), and a whole bunch of SAE.

Ahh.. 62, the last "Pre-unit" Very nice. Post some pics. I helped a friend build a "Triton" several years ago using a 62 engine & trans. We stuck a 5 speed gearset into the old pre-unit box as well. He ran it at Loudon & Daytona in the vintage classes for several years. I just recently threw in the towel and sold my Snap On British wrenches & sockets and my specialty tools on Ebay. Got a couple small things on their now that I keep finding when I did through old boxes of junk in the basement but I have very little left anymore. The Red & Yellow chopper in the pics I posted was my daily ride for 25 years. OOPS... Duh... I just now saw where you said "4 wheeled"... Those pesky Brits using "TR" for cars AND bikes... Carry on