I really thought that I would be dead before going METRIC

[Rustytruck]

I don't mine either system but don't mix them on the same car. My pet peeve is that most fasteners in small size metric are much softer than our standard sizes.

My other pet peeve in my spare bolt bins do not have many metric bolts in them. I go to my spare bolt bins to find project bolts or missing/broken bolts and its a futile effort for metric stuff.

I live within both worlds so it isnt really a big deal. Last year I made a list of my tools and bought all the proper sockets and wrenches in the blended sizes so I could keep my metric and SAE fully segregated. Doubled-ed up on all the extensions and ratchets. I should have done that 20 years ago. Now i can carry just one bag at a time unless I have to deal with my GM carrying friends then its both bags and a mess of crap scattered everywhere.

 

[Skiddy]

I don't mine either system but don't mix them on the same car. My pet peeve is that most fasteners in small size metric are much softer than our standard sizes.

My other pet peeve in my spare bolt bins do not have many metric bolts in them. I go to my spare bolt bins to find project bolts or missing/broken bolts and its a futile effort for metric stuff.

I am the same way

 

[El Kabong]

For years this was my metric wrench set.

 

[kazman]

That's still an imperial adjustable wrench, if it were a metric, it would have 254 stamped on it. ;-)

 

[miikee73]

I have a Dewalt crescent wrench that has SAE etched on one side and Metric on the other.

 

[Rustytruck]

So you have to work the metric side left handed. What kind of BS is that. I'm not left handed. This is just another reason to not go metric. I guess its that way so you stop breaking the metric bolts wrenching on your weak side. If you buy the wrench in Canada is the Crescent wrench engraved metric on the top side?

 

[NC-Fordguy]

I recall having to learn the metric system in jr high school back when Jimmy Farmer was president. The rest of the world was using the system and the US was going to switch over.

40 some years later, I still buy lumber by the foot, gas by the gallon, motor oil by the quart, freon by the ounce, and hamburger by the pound. Last speeding ticket I got was for going 11 miles per hour over the limit.

What sucks about metric nuts and bolts is that on certain sizes there can be 4 different thread pitches. Out with the thread pitch gauge to figure it out.

 

[Apogee]

What sucks about metric nuts and bolts is that on certain sizes there can be 4 different thread pitches. Out with the thread pitch gauge to figure it out.

This is true for Imperial/SAE as well. You have coarse thread, fine thread, extra fine thread, extra-extra fine thread, etc. I prefer the metric method of measuring thread pitch since it defines the minor diameter of the thread, which is your pilot drill diameter. An M10x1.5 fastener uses an 10-1.5 = 8.5mm pilot drill...try doing that with a 1/2-13 fastener. While I can do the math to come up with a .4219 [27/64] drill bit, I certainly can't do it in my head.

Similarly, someone above said that metric fasteners are softer/weaker or something along those lines, and that's not true either. Metric fasteners are available with grade or class ratings, just like SAE, but of course a little different. Class 8.8 metric are comparable to Grade 5 SAE, Class 10.9 metric are just a shade under Grade 8, and Class 12.9 are comparable to Grade 9. I use a lot of metric hardware and have found that a lot of places stock Class 8.8 hardware but not the 10.9, so that can be a little frustrating at times, but otherwise hasn't generally been an issue, even with less common sizes like M14x2 (similar to 9/16 fasteners in SAE).

FWIW, you can download a Starrett Inch/Metric Drill/Tap chart and put it in your garage/shop/toolbox for reference. I have a few laying around in various places for when I need them and don't want to do the math on SAE drill/tap stuff.

 

[Broncobowsher]

It can get even more confusing when you are comparing a US gallon to an Imperial gallon. You hear of European cars getting really good MPG, well they are close to England so they are using the larger Imperial gallon.

I have taps and dies so I can make adaptors between NPT and BPT (National and British) Pipe Thread.

And if you really want a bastard, mix in some Whitworth nuts and bolts.

 

[Apogee]

It can get even more confusing when you are comparing a US gallon to an Imperial gallon. You hear of European cars getting really good MPG, well they are close to England so they are using the larger Imperial gallon.

I have taps and dies so I can make adaptors between NPT and BPT (National and British) Pipe Thread.

And if you really want a bastard, mix in some Whitworth nuts and bolts.

Damn...you sir are dating yourself. Who knew you were 177 years old? I've heard of the British Standard Whitworth thread profile (55 degree tooth profile), but have never seen it in person except maybe unknowingly in a museum. First national thread standard ever if I'm not mistaken, where up to that point, every screw was custom made for an application by whatever company or person made it.

 

[NC-Fordguy]

This is true for Imperial/SAE as well. You have coarse thread, fine thread, extra fine thread, extra-extra fine thread, etc.
.

Interesting. I did not know this nor have I ever run into this in SAE automotive applications. Just course or fine thread. I'm curious in what instances you have run into this?

 

[Rustytruck]

Firearms use allot if extra fine threads.

 

[Apogee]

Firearms use allot if extra fine threads.

X2. I've also run into them on some miniature automation equipment, electronics/switches, valves, pneumatics, robotics, test/lab devices, etc. I rarely see it much in automotive stuff, although I did recently run into an M12x1.25 caliper mounting bolt on a 87-90 Dodge Dakota front spindle...that's basically an extra-fine metric fastener with M12x1.75 being "coarse" and M12x1.50 being "fine".

That said, the UN thread standards I'm aware of for SAE/Imperial stuff are UNC (coarse), UNF (fine), UNEF (extra-fine) and UNS, where the UNS are "special" and tend to be used in proprietary applications where the manufacturer really doesn't want you mixing and matching their stuff with their competitors. These are sometimes extra-extra fine or have some other distinguishing feature that may or may not be distinguishable to the naked eye...I personally am not really a fan of the UN system. Quite often in my experience, it's when I need an exceptionally large threaded hole, something like a 3" hole with 16 threads per inch...or 20...or 28. While you can get custom taps, these parts are typically turned in a CNC lathe or made with helical thread milling in a CNC milling machine. A good real world example of something like this would be the hydraulic cylinder/ram in my 55-ton press, which is threaded on the one end to mount into the cross plate, and must be able to withstand 55-tons of force.

IMO, just make it explicit and call it by what it is. If it's a coarse 1/2" bolt, then call it 1/2-13. If it's fine, 1/2-20. Extra fine, 1/2-28. That way there's no doubt as to what it is, and what you need to accommodate it.

Metric fasteners are always explicit as far as I know, so they specify diameter and pitch rather than having an additional classification for thread pitch category since that relative and arbitrary anyhow.

 

[Weevil]

Reality

Problem with the metric system is it is not the same from country to country for fits , as in threads . French bolt Italian nut maybe no workee workee.
Build everything DIN Standard "German "
It will probably work . Then there is that other thing

 

[Apogee]

Mars Climate Orbiter burned up in the atmosphere due to a US/SI unit conversion error. I know we've been using the term "metric" in this thread pretty loosely, however it is technically the SI system, which is the modern and universally accepted form of the metric system in use today.

I've never had any issues with cross compatibility between fasteners, but most of my metric stuff seems to come out of Taiwan. I haven't spent a lot of time thinking about thread fit classifications, mostly because it hasn't been an issue. I run the typical common fits for male and female threads and have never had an issue, even with electro-plating factored into the equation.