The Mid Tompkins front sight has been discontinued and been replaced with a much higher quality machined front sight. These sights, unlike the Tompkins sights, will accept a standard 22mm German iris. The MCS101 model will work with either the metal inserts (#MCS104) or the 22mm iris. The MCS103 level works with either machined front sight. They fit on a standard dovetail. Threaded on both ends.