57 front bumper frame bolt type?

[TR1957]

I am installing a new front bumper on my 57 4 door post sedan. I am using the old mounting brackets which I refinished. For some reason, I lost the 4 bolts which attach the bumper to the frame. In the assembly manual they are part number 123905. But I can't find any documentation which says the length or type of bolt it is. Does anybody know what the bolt type and length is? Thanks! - Tony

[carls 56 (RIP 11/24/2021)]

danchuk says they are 1-1/4". www.danchuk.com (http://www.danchuk.com)

[TR1957]

Yes that will work. I had some bolts left over when I reassembled the bumper but didn't think they were the right ones. After re-inspecting the mounting holes, they don't have to span the width of the frame because there is a recess to put a socket wrench into the frame. So a 1 1/4 will work fine. Thanks carls 56!

[chevynut]

For some reason GM increased the diameter of the holes in the frame where the bumper bolts on in 1957. My guess is that was for adjustability of the bumper. In '56 they used 7/16" bolts in 7/16" holes in both the frame and the bumper brackets, so there's almost no adjustability. I think the 57 frame holes are 9/16" but I'm not sure what the bolt diameter is.

[TR1957]

here is a picture of the bolt with its castle nut. total width of bolt is 9/16", length is 1 1/2".2423

[c57heaven]

here is a picture of the bolt with its castle nut. total width of bolt is 9/16", length is 1 1/2".2423

correct.

[chevynut]

here is a picture of the bolt with its castle nut. total width of bolt is 9/16", length is 1 1/2".2423

That bolt is only 1" long. Bolts are measured from under the head to the end.