It is the peep sight with the screw on the side instead of the knurled knob on the side. It is listed under "peep sights" on the upper right of their "Home" page. As soon as I get the pictures onto a wen site, I will post them. The gunsmith installed a small rib on the barrel for it. It worked out well as long as you are never going to want a scope.

On my .458WM ruger No1, I installed a small scope because the front sight was getting lost down in the "V" of the open rear sight. Just my aging eyes, I guess.