These are original, new and unissued, 'Screws, Ejector B' for the .303" SMLE Rifle No1 MkIII & III*. 

These fit through the left side wall of the receiver. The tip of the screw protrudes into the bolt way so that the left edge of the cartridge rim catches it as the bolt is pulled back tipping the empty case out of the right side of the rifle.

Unit of sale 1 screw. British Army Part No BB0733. Stock No EFDSMLESP36.