I realise this isn't what you were referring to but the No1 MkIII ejector screw is NOT the same as the No4 ejector screw.
The No1 MkIII ejector screw is a 'special' Enfield thread.
Comprising 0.1656" diameter x 37 tpi.
The original length was 0.205" but was later replaced by one 0.23" long.