correct size sill plate screws

[Ronald L.]

Re: correct size sill plate screws

Gary,
I think you are seeing a concave or dishing instead of a straight V taper. Could be onto something.

[Michael G.]

[Mark P.]

Here are the two sill plates from my 65. The sill plate I believe is original is the dirty and scratched one in all pictures. The reproduction sill has shallower countersunk holes and the two sets of indented lines are finer on the original (13 grooves) versus the reproduction (10 grooves). When I set an original screw into the original sill hole it is proud about .045" and when I set it into the reproduction sill it is proud about .080". I used a depth micrometer and it was a bit tricky due to the concave screw head. I measured multiple times and the .035" difference was pretty consistent. I was a machinist trainee for just two years so I am far from an expert.

[Alan D.]

Remember that the 63 and most 64 sill plates use different screws then late 64 - 67 sill plates.
pn 9417945 was used for the 4 hole, while later pn 9414766 for the 6 hole Both of these were 10-16 1"
However the 4 hole had a bigger head, when the 6 hole was used the smaller head was used (as I recall)

So if the car is early 1965, larger head screws could have still been in the bins, the difference is very visible.

[Gary B.]

Alan,

Yes, GM 9414766 have a #10 thread with a #8 head.

Gary