[will slow gto]

I'm having trouble recalling which style fastener to use re-installing the splash shield and brake hose brackets on my 69 GTO. It seems to come down to one of these two in the photo. One has coarser threads like those used to attach sheet metal to the valance and is 7/8" in length (minus head). The other fastener, with the finer threads is very similar, if not identical to those used to hang the mufflers, 3/4" length. Here's a photo of the two competing fasteners and the splash shield and brake hose bracket areas. Thanks...

[dataway]

I recently did the same job, I used the nicer looking machine screw for the brackets (the rubber hose to hard line bracket), and I think the splashed shield also used the nicer screws. I think the pieces with the wood screw looking thread were used on the line brackets ... oh **** .... I'll just go down and look ....

On my 68, the hose/hard line bracket, the splash shield, and the brake line hold down clips all have the nicer machine screw type ... not the pointy ended type. Although I know dang well I used the pointy type somewhere in there.

Usually you can tell by the holes, the nicer, flat ended machine screws will have a hole in the frame which is nicer, more threads, more metal "punched" into the frame and threaded than the holes made for use with the pointy screws.

[Blowd]

Just FWIW the screw you have pictured on the left is a "sheet metal" screw which cuts threads as it goes. The one pictured on the right, I suspect, is a thread rolling screw. This can be verified by looking at it's blunt tip. It should be sort of 3 sided. The thread rolling screw forms threads in heavier gauge steel with out making chips.
The short version of this is; the screws on the right go into the frame holes, the ones on the left go into sheet metal parts.