I bought a used 870 that is my primary hunting gun now, and it came with some kind of fiber optic sight that is awesome. Never comes off. It goes over the bead on front.
A friend bought one that looks like mine, but it wouldnt stay on his gun without black tape.
I love mine tho I dont know what kind it is. Its kinda fat. I sure pick up the targets fast without even thinking about it.
My turkey gun came with a set of fiber sites, but I'm going to replace them with a better set in the spring.