[ f342 ] Unusual sight Military marked wire cross hairs

Description

Unusual Brass sight Military marked with crude wire cross hairs, the gent whom I bought this from said they were for the front sight of a 303, the small catch opens & allows you to screw & attach it to the existing front sight of a 303 rifle, I personally have never heard or that nor seen it before, when you look at this piece it does make sense, it is well marked with Military acceptance stamps, as well as what appears to be a makers mark,
It could well be something used in or on one of the many artillery sights that exist out there, I would love to hear your opinions on what this is actually for as its quite unusual.