It fits fine on a 40 breeder, I have them off. ecause I have a glass lid but put them on to show. The light weighs like 2 pounds and if u screw the side screws in it is unlikely to fall off. By the way the tank is the standard petco 40b
Thank you so much for sharing! Glad to read that's a petco 40 breeder. is that the 36" fixture, I'm assuming?