Before you start making caps from scratch, I'd suggest that you investigate the myriad of plastic bottlecaps that are readily available in the supermarket or drug store. I front-capped my Jupiter 8 50mm f2 with the plastic cap from a large bottle of grape juice. By grinding out the threads with a Dremel, the cap fits snuggly. And the backcap came from the sliced off tip of a Zero Fabric Softener cap that had the slots for the three mount tabs cut out with an exacto knife.
Whenever possible, I keep the lenshoods mounted on the lenses, even when they are being stored, and the cap for the hooded Jupiter came from a generic plastic storage bottle that was purchased in a dollar store.
Again, the threads were mostly ground out, leaving only a few short lengths to grip the hood when mounted.
A couple of coats of Krylon black spray paint, and voila. Done and done.
