This is a 7/8 in. tub and shower door nylon ball bearing roller with a flat edged wheel. It has a threaded hex head hub that uses an 8-32 x 3/8 in. long Phillips binder head machine screw to fasten it to the door bracket. Used on a variety of different tub and shower top roller systems. If you require a larger roller use Prime-Line part M 6001 for 3/4 in. flat roller.