REAR BUMPER to FRAME attachment BOLT THREAD discrepancy

[sdb8100]

Hello,

I have a '69 roadster that I am at the point where I am bolting up new bumpers front and rear after years of restoration.

I have 2 of the 4 bolts for the rear bumper bracket-to-frame and was looking to replace with nice new hardware.

Upon measuring the thread, it appeared to be M10X1.0 PITCH. HOWEVER, when I grabbed the new M10x1.0 bolts and went to thread in, the diameter seems too big and wont thread in.

Searching the forum and Techwiki I've seen reference to both M10x1.0 Pitch and 3/8x24. The diameter of 3/8 seems to match closer when I put a caliper them, but the thread definitely doesn't seem to want to work.

Any insights are welcome.

[Habitat.pat]

You say you are installing new bumpers. Are these new to you, new OEM, or the Vietnamese stainless bumpers? If the Vietnamese bumpers, I can go see what fasteners they use because I have them on my car. I can check in the morning.

Peace, Pat

[david premo]

I fairly confident that 3/8’s fine thread would be correct. Most everything on the chassis and body are SAE threads. A few exceptions on the 68 and on bodies, though I am fairly confident all of the frames for all of the years are SAE.
Dave

[JT68]

Again, Dave is right. 3/8SAE - Not Metric.