The Screw Plate. Cutting & Sizing Thread Pre - Whitworth Standard of 1841.

These are what Ken refers to as screw plates, we are not sure what date they hail from, only what they are used for. They are plates which have a variety of screw die cut sizes for making pins for guns from small to large. These are the forerunner to the modern screw thread die you see at top right. Joseph Whitworth standardised thread sizes in 1841 so these probably hailed from earlier days than this and were continued to be made and used in the trade for when old guns with bastard or non standard threads came in for repair.

By Simon Clode

The procedure for cutting the threads was much the same as with modern die cutters. A piece of silver steel was turned to the correct size and run through the chosen slot in the screw plate. The increments in size were small and many on these screw plates fall between the now standard BA sizes.

To make a corresponding tap for the female thread for the pin made another largest diameter piece of silver steel is run through the die and then small slots are ground vertically up the cut thread, the whole then hardened and tempered to cut the female thread size.