There are a few car parts that despite the widespread adoption of the Metric system remain sized in English units as international standards.

Think about it - A few of the known parts in the next post...

OK - for those of you playing at home, we have

1) Wheels (e.g. 15", 16" ...)
2) Brake caliper mounting bolt spacing (per the brake thread) - 3.0" and 3.5"
3) Brake master cylinder bore. Our "19mm" is really a 3/4" bore, and the other familiar sizes (17mm 20,5mm 23mm) are actually sized in 16's of an inch
4) Seat Belt mounting bolts. They are really 7/16-UNF (24 tpi). This is close to an 11mm 1,0 to about 3 decimal places so they're effectively interchangeable. But 7/16-24 they are.

Interesting topic. I knew about 1, 3 and 4, but never really thought about 2.

This is really a stretch, but what about Wiper blade lengths?

So in addition to what, how about why?

1) Defacto standard? Does anyone today use metric wheel sizes or is the entire world pretty much on the "inch" standard?
2) Off the shelf ATE design? Question is, why would ATE use English vs. Metric?
3) Same as 2.
4) Is this an agreed upon standard?

IIRC Michelin has tried from time to time to introduce various proprietary metric tire flavors throughout the years. They sold Ford on it maybe 20 years ago. TVR? something like that. Extinct.

I believe Bendix patented the now-familiar hydraulic brake system and licensed it to the world. Terms of the license to ensure international commonality, I believe.


I recall (but I could be wrong) that it is an ISO standard, but it could just be a SAE. In any case - the whole world does it and has since the introduction of the seat belt.

Even your 914 :-;

When I was putting in a temp brace between the upper seatbelt mount and the upper door hinge mounts (for rust repair purposes), I kept trying different metric bolts and I couldn't get any common ones to fit. I kept scratching my head as to what weird metric bolt they would have used for the seatbelt mount until I looked at the stock belt bolt discovered it wasn't metric!

Sort of OT, but for several years Chevy made their engines with bolts with metric heads and SAE threads. They were required to change to metric but hey didn't want to re-tool their engine building equipment so they just changed the bolt heads.

One thing I have found living over here is that things like pipe fittings and air lines all use NPT sizes. I was trying to figure out some plumbing fixtures in my house and all of the sizes ended up being "normal" for me.

i worked in g.m. dealership in the late 80's and had to keep a FULL set of oddball metric and set of std. hard to locate bolts just for that!!! a 3.8 v-6 would come in for a long block we'd all hide, ya never knew what you were in for

G.M. = "gods mistake"


remember in the early 80's the mustang gt's had a metric rim size between 14" & 15"? it was known as the "TRX" wheel. ONLY michelin produced a tire. i bought ALOT of used tires in those days!

mike

IIRC there was an optional Audi wheel (or aftermarket) that was metric too.

Not Audi. At least not after 1969. Had to be BMW. Cheaper now to buy a nice set of used wheels AND tires than to buy metric tires ..................................

The Cap'n