The rear sight Sarco sent me will not fit on this base. This base is too tight to let the rear sight spin under the tab. The sight could not be spun using the knob (or a tap hammer). This is junk. Filing will be needed to make this work to open the clearance. The only reason I gave it 2 stars instead of 1 is because it’s not rusted.
Nice item, fits good. Dose not come with collar pin.