Can you provide a photo? The lock screws I know of are closer to 2BA than 7BA but might be 1BA or even 0BA. A photo would tell me whether I have one here to measure.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.