What is the Lee Enfield wrist thread on the side?

[ovenpaa]

This is a bit convoluted however here goes....I have a Lee Enfield with the BSA type safety with safety spring attached by a screw that measures as 5/32" x 36tpi screwed into the strap however some references show this as 37tpi.

I ask because I need to make or source a screw to hold my 'Central' aperture sight to a Parker sight bracket and I am not totally sure what it is however the existing safety spring screw seems to fit. Alternatively does anyone have a spare retaining screw ideally knurled to attach an aperture sight to a Parker bracket?

[waterford103]

If it's 5/32" x 36tpi 55degree whit then it's a cycle thread I think.

[ovenpaa]

5/32 cycle thread is 32tpi, I remember it because everything bigger is 26tpi and I probably have a tap here from my years working pre war British motorbikes. I checked again and it certainly seems to be around 36tpi. I will dig some suitable material out and screwcut it at 36tpi and see if it screws into the sight fixing plate which looks to be a Parker SP1