Is this ordnance related?

[Fragman]

Hi. A friend has asked me to try and ID this item. We're not sure if it's even ordnance related, but it does have some similarities to other know items. Cheers

 

[ammofo]

Quick answer - I DON'T KNOW....
Observations - the cross hatchings on the 'bolt' head are clearly designed to be tightened/untightened by finger and thumb. That makes the presence of the ring unusual from a practical perspective as it would surely get in the way when turning the bolt. It would appear to be some kind of adjusting screw rather than a securing bolt, but for what I DON'T KNOW !!
If it WAS ordnance related it might be related to a large gun sight, but it could just as easily be off a Robin Reliant !!
I will keep an eye on this one...