Ross Bridge Sight Base ID.

[Lee Enfield]

Here are pictures of 2 rifles fitted with the same type of sight.
The pictures are out of order, there are 2 different sight bridges, and one of them seems to be the same sight bridge as you have.

MkII** Military variety rear sights and bridges

the 7 on your sight is a military inspection marking, apparently this indicates that your sight was manufactured for a MkIII /1910 military rifle

The H.W.C. marked sight was made by the H.W. Cooey Machine & Arms Co. in Cobourg, Ont. Those not H.W.C. marked were made by Canada Tool & Specialty in New Glasgow, N.S. I stand to be corrected, but believe those were the only two manufacturers of those particular sights.

That's what I thought too, but I found a photo of an almost identical sight labled as BSA IIRC - I'm trying to back track to find the source.