I am with burnt and JC Kelly here. Back the 1970,s I took two 3 inch long pieces of 3/4 inch round mild steel, in one I drilled a 3/8 inch hole in one, a 5/16 hole in the other. The edge of both holes were about 1/8th of an inch from the edge of the 3/4 rod. I radiused the larger rod down to the edge of the hole, then silver soldered a piece of rod of the appropriate size into the hole. I have made dozens of entry thimbles since then depending on the size required and use the same fixtures I made back then, today. Just remember to keep your brass annealed while forming and with a little practice and some judicious hammering and filing, they will turn out fine. I think it helps if you try to think like the original makers did. I imagine they probably forged something out on the anvil in a few minutes when they were apprenticing, and used the same fixture their entire career.