Why is my seatbelt mounting not metric?
 

My belt mounting is 7/16-20 hardware, is this some Nader American standard for belts or something?

Good old DOT specs.

"I am from the government and I am here to help you."

The same reason the speedometer stopped at 85 MPH for many years.

I think they are a bastard size to prevent people from replacing them with cheap bolts. Probably a good thing.

Cheaply made 7/16-20 bolts can be found if that's the objective. Naw, it's DOT spec for the multitude of cars purchased in the states.

The correct bolt is also easier to find than an equvalent high strength metric bolt (~ M12).

Sherwood

But not easily. And not at Home Depot. Unlike metric or inch bolts.

Why would the DOT care about commonization?

Mounting harnesses are we?;)

ALL safety equipment in the US has to be DOT approved, and in the US, SAE is standard, so that's what was spec'd including mounting bolts.

Headlights, brakes, seatbelts...

Technically our H1 and H4 headlights are illegal for use on public roads; no adjusting tabs. For quite awhile, ONLY sealed beam headlights were legal, a throwback to the crappy lights earlier in the 1900's.

The 85 mph speedos (with highlighted '55') were dictated for supposed fuel economy by the NHTSA under Jimmy Carter on all cars sold in the US. Lasted for about 3 years 80-82. Many Pcars of that era have had their speedos replaced w/ 150 mph units.

Michelin developed radial tires and used metric units of measure.

In the late 70's Michelin developed a metric wheel/tire size (TRX?) That I think only appeared on SAABs, Jaguars and some 'sporty' Ford models. Were expensive and did not catch on. Were roughly a 15-1/2" wheel, I think. Avon, I think also made the tires, too, for Jag.
Disappeared after 10 years or so.