Parker-Hale backsight?

[Surpmil]

It looks like someone has put in a screw or probably a spring loaded plunger/ball to tighten up the elevation slide. Or perhaps that was a late attempt by PH to improve things I don't know. Never seen it before myself.

If the knobs are 'home-made', then whoever was doing it would be well able to do that kind of modification as well.

Still doesn't solve the lack of an anti-backlash spring on the windage screw.

I've got one of the alloy bodied ones here and it is a POS compared to a Central or Twin Zero, or an early PH5 for SMLE for that matter.

Only the quality of fitting on the Twin Zero makes up for the fact that it has a rectangular elevation slide and slot: emphatically NOT self-aligning in principle. Probably done to get around PH patents...guess I'd better get Edna's book and 'get edumacated.'