We need to see if the round arms are threaded into each other. It's probably the tool used to hold the backsight slide when replacing the pin that locks the threaded deflection knob to the threaded part.

Armourers were issued with plenty of these tools - think of the various tools for removing the L1A1 extractor or the forked screwdriver 'supposedly' used for replacing the stem nut on the Bren carrying handle or the so called alignment tool for the....... - anyway, you get my drift...... I mean, has anyone ever seen the totally useless, complicated, expensive and OTT tool, said to have been devised and issued for the removal of the M1919 driving spring?

It was probably one of those sorts of tools that you used during your apprenticeship, saw again once when you were out in the REAL world, saw how the job was REALLY done by an old, wise Armourer using his own home made and FAR simpler too. Then you made something similar and simpler which you still have. The issue tool stayed where it was in the 'A in U' cupboard forever or until the workshop closed down.

Other very similar tools were the foresight adjusters...........