Spark plug wire question

[Charles in SC]

I am in the process of shortening my plug wires. On the plug end there is a contact spring that screws onto a straight wire piece that is inserted into the plug wire core. Is there a tool designed to hold the threaded end so it can be held securly while being pushed into the wire core? I am thinking about maybe a small thread die. The thread is about 4-40. Thanks in advance!