Cheap sites. You get what you pay for. One of the holes for the fiber optic tube on the rear sight was way too small, so I had to spend some time reaming the hole before I could even install the fiber optic tubing. I installed the sights on my WE G17, and there were some fitment issues. The sights didn't come with any screws, and the screws used by the original WE Glock sights were slightly off spec. I had to dremel the front sight screw a bit, so it would fully screw into the base of the actual sight itself. The square insert on the front sight is slightly smaller than the port on the slide it's meant to be seated in, so the front sight wobbled a bit, I just used a bit of gorilla glue to keep the front sight centered. The screw for the original WE Glock rear sight was too skinny, so I had to find another one in my collection of random screws. They look great, once I got the damn things installed properly, and they aim true at about 10 meters or so; I haven't really had the chance to test them out at any greater distance yet. For the price, they're not a bad set of sights, you just may need to go through some headaches to get them installed, depending on what brand of Glock you have.