I have the hard to find Thompson Center Primitive Rear Sight for sale. This is the Part #907 they sold to convert your octagon barreled rifle from the adjustable sight. It fits the factory drilled screw holes ( approx. 1 7/16" or 1.470" ctr. to ctr.) You use your existing sight base screws to mount it. This unit has not been used or altered. I am asking $60 plus shipping (USPS Priority is $8.50). I take credit/debit cards by phone or USPS Money Orders.