1/4 X 32 thread. From Jim Chambers. Extra large, deep inside cone improves ignition. Unit is installed using a vice grip, then shoulder is cut off with a hacksaw.
The large cone of this touch hole liner brings the flash to with in a few thousandths of an inch of the main powder charge which will noticibly decrease the ignition time. Use #4 drill & 1/4 x 32 tap.
