I guess that heading just about covers the question, the early Heinze ( wood ) coil box nut to fasten to the firewall, has 4 chunky old style nuts ( somehow l have lost 3 of the 4 ), and would like to know what size they are, our local bolt shop has no idea, ....we know its a 5/16" ....... that's about it.
Anyone got any spares ???
They are a brass (plated steel) hex nut 5/16" x 20 tpi, 19/32" across the flats and 0.330" thick. That thread is unique to the Heinze box. I make them if you need them.
RV makes good stuff. I have quite a few of his bolts on my cars.
The 5/16-20 thread tap and dies are available at most online tooling stores as a "special size" and not really too expensive. Many a wood box Heinz coil box has been found with 5/16-18 threaded nuts having been cross threaded in place or at least stuck on the stud ends when they didn't go on more than a couple of threads.