To set the line 20 small jacket snaps, you need to first punch a hole in the leather for the snap cap and another hole for the snap post. After each are inserted into the holes, place the socket over the snap cap post to be set. Under the snap cap, you will need to place a concave anvil so the cap keeps the nice curve when you set it. To do this, you need a setter to hit with a hammer that will crimp the metal snap post around the inside of the socket. The snap setter required for this size line 20 small jacket snap will not work with the larger size line 24 snaps. However the concave anvil will work with both this line 20 small size snap and the larger line 24 snaps.
When buying snaps, the thickness of leather must be considered. These small snaps work great with 3 - 6 oz thick leather. An oz is about 1/64 inch thick.