Nate;
Most original Berks County horns that I've handled had relatively coarse threads, when compared to other varieties of shop made screw tip horns. Sometimes this type of thread is called "box" threads, or wood thread. I've handled original Berks horns with 1/2"-8; 9/16"-9; and 9/16"-10 threads.
For replicating Berks horns, I use 1/2"-8 thread. You can purchase a 1/2"-8 tap for cutting internal (Female) threads in wood from several sources such as Woodcrafters, etc. This tap will work fine on horn. The male threads on the screw tip can be cut with a metal cutting lathe, or a 1/2"-8 die, if you can find one. I have very carefully layed out these threads and then hand filed them with a triangular file. This produces threads that closely approximate the originals, as many of the original tips I've seen have what appears to be coarsely filed male threads.
A source for custom made taps and dies is a company called TapcoUSA. They have a website, and are located in the Chicago area, if I remember correctly. Currently I am using a 1/2"-8 die produced by this company for my Berks horn work.
Art DeCamp
