Standard Coupling Nuts
The critical dimensions required to identify a coupling nut are the thread diameter, threads per inch, bore and size of hex from flat to flat. Be sure you have accurately measured the outside diameter of the thread on your punch stem and determined the threads per inch, preferably with a thread gauge.
Coupling nuts are designed to be turned on the stem by hand and then tightened with a wrench or spanner wrench. Over-torquing may cause damage to the threads. Check periodically to ensure that the nut remains tight and the punch cannot move up and down, a major cause of punch breakage.