The B-Square mount for the No4MkI rifle replaces the rear sight and is secured at the front by replacing the ejector screw. Fitting that screw is about the only "smithing" you have to do. The rear pin is secured by the installation of two, very tiny, E-clips. They are easy to install and easy to lose when unpacking the mount. This mount comes complete with 1" rings. The problem with B-Square is that you're pretty much limited to whatever stock is in country since they no longer ship to Canada.