Mark 1 Sight Question

[sop2510]

I installed a Mark 1 sight on my Lee-Enfield No. 4 Mk. 1. Can you give me any information on this sight?

Left side: Letter "B" with an arrowhead beneath it.
Top of sight: Letter "B" with an arrowhead beneath it.
Adjusting knob: Letter "B".
Right side: Letter "B" with "CR" beneath it and "670" below that.

Bob in Roswell, GA, USA
"A town with beautiful horses and fast women"

[Thunderbox]

BSA-made sight, with a post-WW2 ordnance part code "CR670"