Searching for enhanced sights for my Colt Defender, without requiring machining of the slide presented some difficulty. I really wanted a combination fiber optic/tritium sight similar to what I have on my CZ-75B. (Tru-Glo) The only sight set I could find was made by XS, using a ball and post type sight. I bought a set, thinking that I could work with the system. The tritium inserts in these sights are very good, I can see them glowing across the bedroom at night. The sights fit perfectly with no alterations. It appears as if this Colt uses a Novak rear cut, and a propitiatory, over-sized front cut. Why? Who the hell knows..... The big problem is that I just can not get the hang of "dotting the I." I don't shoot the pistol worth a damn with these sights, even though I have given them a good try. I was wondering if anyone here has used the system and how it worked for others. On paper, the system looked really good to me. In practice, not so much.