1970 Front Bumper Bolt Finish

[Allen N.]

I have read thru the old threads and cannot determine the original finish for the bolts that go in the corners of the front bumper. My car was built in early 1970. The GM part number of the bolts is 427559. My reading of old threads has me leaning towards black phosphate, but the ones in my car are cad or zinc plated. They are 3/8" X 1-1/2" grade 5 with a P head marking. My car has been repainted in the past, so the bumpers have been removed before and so my bolts may not be original.

Thanks,
Allen

[Gary B.]

Re: 1970 Front Bumper Bolt Finish

My guess would be black phosphate. GM would not have spent the extra $$$ for zinc or cadmium that is not seen. Maybe Dave Bartush will chime in, he has a book on GM fasteners and there finish.

Gary B

[Joe L.]

Re: 1970 Front Bumper Bolt Finish

I have read thru the old threads and cannot determine the original finish for the bolts that go in the corners of the front bumper. My car was built in early 1970. The GM part number of the bolts is 427559. My reading of old threads has me leaning towards black phosphate, but the ones in my car are cad or zinc plated. They are 3/8" X 1-1/2" grade 5 with a P head marking. My car has been repainted in the past, so the bumpers have been removed before and so my bolts may not be original.

Thanks,
Allen

Allen------


GM #427559 was a zinc or cadmium plated bolt. It was 3/8-16 X 1-7/32" and of GM 300M material (SAE grade 8).

[David B.]

Re: 1970 Front Bumper Bolt Finish

GM #427559 3/8 - 16 x 2" Zinc GM 300 M class 2A thread

[Allen N.]

Re: 1970 Front Bumper Bolt Finish

Thank you very much for the help.

[Joe L.]

Re: 1970 Front Bumper Bolt Finish

Thank you very much for the help.

Allen------


How long is the bolt? Dave and I seem to have different specs on length.