This is a "E" tab tandem roller assembly with two 1-1/2 in. concave steel ball bearing rollers. As the corner screw passes through the "E" tab it captures the roller assembly and positions it in the door's bottom rail. The housing is 11/16 in. wide with a 7/8 in. flare, 1-3/32 in. tall and 3-1/8 in. long. Used by Fleetwood and a variety of other sliding patio door manufacturers.