It's the size of a standard diameter laser. UTG laser mounts are the same diameter, etc. Just a warning though, that laser mount sucks. I had one on my ATI and the way the thing is designed you can't really tighten it down on the laser. They use wood screw looking things that thread themselves in the plastic, so even if you C clamp the things down before threading the screws through, it still doesn't get as tight as if you ran a screw through there and used a nut to tighten it down with. I've since sold my ATI and gone back to the factory stock, put the laser in a UTG mount and put it on my WASR-10.