A friend has a nearly antique Stevens Nitro Special shotgun. The screw that holds the forearm stock to the barrel had been bent and it would not seat fully. (See the blue arrow for the location of the screw.) He had been to a gunsmith who told him it was not any standard size and would be almost impossible to replace.
(This photo is from gunbroker.com.)
Step 1: The Screw and Its Receiver
If I had known this project would turn out so well, I would have taken photos as I went. The drawing shows a block of steel about 1/2 inch by 1/2 inch square with a tapped hole to receive the forearm screw. My best guess is that the screw was turned partially into this block attached under the barrel of the gun when the gun or the barrel was dropped and the screw absorbed the impact. Anyway, the screw would turn into its receiver only about three turns before it would go no farther. The result was that the forearm stock was loose on the barrel.