Here you go John, measurements are a guide just adjust to the stock you have to hand. I tapped the thread 12mm, but anything over 6mm should be fine. Acetal, Delrin or Nylon would do for the soft end. If you only have a short bit of brass, the body can be turned in steel or alloy and mirror the threaded end. I used a light knurl so it has quite a flat top, then you can use beer can to grip the body for the recesses to clean up the knurled area (10mm gaps)
LOL, the 1.5mm should be 2.5mm on the soft insert, and of course, all dimensions in mm, Unless you want a really BIG hammer.