I bought a BT-99 that came equipped with this Keen Sight rib. It is 3/8” wide and 29 ½” long. It is ½” high at the receiver end and 1/8” high on the barrel end. It has a small bead at its’ middle. I looked on the Keen Sight web site and found out you attach it to your Rib with silicone sealer. You have to take off your front bead and reattach it through the Keen Sight rib. When I removed it from the BT-99 I just pulled some 20 lb. fishing line under it to remove it. I don’t know what they cost new, but I will take $50.00 plus shipping to your zip. Email me for pics.