PART NO.  SPL.PAGE  DESCRIPTION                                                           
17H5383   16.N.3    Screw -fixing lever -(flasher switch, switches, 1600 and 1600-MK-II)

This is the securing screw for the bat handle on the turn Lucas signal switch (with vacuum delay shut-off). It is a Cheese Head screw, number 5BA thread, 1/2 inch long. I believe original screw head was slightly crowned on top, and it should be bright nickle plated for appearance. Some modern replacement parts may be flat on top (common modern cheese head) and might be zinc plated (dull when new and fading darker with age).

Some modern replacement switches may have metric threads and metric screws, amd those will definitely not be interchangeable. If you buy a new switch, the original screw may not fit, and if you are going to buy a new screw, you need to know if you need the original 5BA screw or a modern metric screw, definitely two different part numbers.