The adapter is made from parts I bought at a local Lowes Home Center: the body, a bronze 3/8 x 5/8 x 1" sleeve bearing; the "base" is a 1/4-20 nail-in Tee Nut (the hammer-in ones have flanges which will get in the way). I cut a section off a brass 3/8 x 16 bolt and used it for the 3/8 side.
I epoxied the tee nut in the straight end of the bearing first. The tee nut gives this adapter a nice flange for stability on the tripod head.
After the tee nut epoxy cured, I then epoxied the bolt piece into the flange end of the bearing, leaving about 3/16" of the bolt extending beyond it.
Once that cured, I had a sweet, compact little adapter to put my antique camera on a tripod.