Most of the original bolts from my 1954 XK120 are in good shape and reusable for the restoration but there were a few dozen whose heads are corroded to the point they’re not presentable. This is a couple of the worst after cleaning up with glass beads in the blasting cabinet:
The threads are in good shape, so how to restore them so they’re presentable and suitable for use in less visible areas? Answer, cast the patterns in epoxy.
This is a collection of some of the better bolts fixed in the bottom half of a mold box
The top half is a quarter inch deep and fits inside the bottom after being filled with a silicone molding compound, this particular kit purchased at Michael’s but any hobby shop will carry it
closeup of the resulting mold - sets in 3 minutes and takes another 20 minutes to full cure - this is really tough, flexible stuff. It sticks to nothing and nothing sticks to it. No mold release agent required.
Back to the very rough examples. I ground off the remnants of the old pattern then grit blasted them to provide some tooth, along with about 30 other restoration candidates
These are given a thin smear of epoxy and pressed into the mold. The silicone grips them tightly
The pair fresh out of the mold
and after a shot of semigloss black
I’ll use flat black epoxy primer to replicate black oxide, keeping the best, unrestored originals for higher visibility, body colour presentations such as found securing hinges.
There are some apparent limitations. I don’t suppose these restored bolts will take much wrenching before the epoxy gets damaged, tough as the stuff is. You also can’t cad plate them, but there aren’t many cad plated bolts used on the 120 anyway.
One can also, of course, replicate the bolt head pattern on new UNF bolts. Not so much repros as counterfeits, though.
Maybe a commercial application © here but easy enough to do yourself.
The mold box took an hour to build, the mold itself another half hour, each batch of bolts, using JB Quick, another half hour or so. Faster than scouring flea markets and eBay listings.