Gang,
I recently picked up a new old stock diecast chrome leading edge for my '66 Starfire. It's always fun to find a perfect 58 year piece of GM trim.

I know you guys like pictures, so here's what this piece looks like installed:

Shiny! But studs on the back can break if you're not careful

All the ones I've collected from the boneyard have broken studs, are badly pitted, scratched or otherwise not so nice. Many were broken, many I just left in the boneyard 30 years ago.

The system GM used consisted of unthreaded mounting studs cast into the chrome, fastened by thread cutting nuts with rubber insulators every few inches from to fasten the trim piece to the car's body/fender, etc. Here's what that system looks like from the back:


Typical GM Mid 60's diecast trim and mounting fasteners. Good system, but hard or expensive to repair. You can tell this is used part from the previous cuts in the mouting post / stud.

This type of nut is designed to cut threads into the relatively soft metal of the diecast trim. If the trim has been on & off a few times for repainting or repair, you should know that these mounting studs don't like to be cut twice. Some people unfamiliar with this system can over torque and snap off the studs when reinstalling. I did this several times along the way and it's a killer when it happens. Especially these days for '66 Olds big cars. If you want to be extra careful, consider a light film of oil on used mounting studs.

This time around I was working with a known-new piece, so I actually tapped my thread cutting nuts flat again. If you're in the market for NOS pieces, look that the piece you're buying has no witness marks from previous installation. Mine was like that- totally smooth (aka new) mounting studs. So, in this case, I actually flatten the thread cutting nuts so they'd bite and properly secure the new piece. The more typical situation is you're working with used parts, in which case _don't_ flatten the cutting teeth.


For new parts, 2 simple hammer taps can restore the cutting threads. Don't do this when working with used diecast chrome.

If you restore the cutting threads and use them to re-cut already used chrome, you increase the chances of snapping a stud weakened from previous use (aka previous installation).

GM used rubber insulators like this to keep the chrome from squeaking on bare metal. They may have helped reduce rust too. If yours are gone, you might want to make new or use 3M dum-dum or similar, though that would make a gooey mess.

Here's what the thread cutting nut and related insulator look like. The other nut is just here to show that GM did these in many sized from 1/4" head, 5/16"'s head, 3/8's head and 7/16's head. I go by the nut driver size which I'm sure is wrong, but that's how I think of them - what tool should I use to fasten it?

Typical mid-60's GM thread-cutting nuts and rubber insulator

Having broken a fair few mounting posts / studs in my time, this time I used a nutdriver. If you can physically fit that tool to get the work done, it helps you feel the cutting process and not go too far in torquing the thread cutting nuts too tight.

A nutdriver is better than a socket wrench if you have the room. Either way be careful.

The last item here is just to say put the piece on the car & put the mounting nuts on loosely, then get the trim piece lined up so it looks right from the outside. For this nose piece there must have been 10-12 studs. I worked from the center of the piece out to the edges so that all the holes lined up and nuts were snugged down consistently. As it happened the trim piece ends wound up with just a little tension on it, but nothing broke and the car looks better than it ever has.

Of course, no one will ever know the difference but me.

Cheers
Chris