This is a 3/4 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 Philips binder head machine screw to fasten it to the door bracket. Used on a variety of different tub and shower top roller systems. Use Prime-Line part M 6003 for 7/8 in. flat roller.