These shower door rollers are constructed of a durable plastic and include an #8-32 threaded hex hub manufactured into each wheel. Wheels like these are used to replace missing or damaged wheels on shower door roller assemblies and the like. These rollers feature a convex (round edge) wheel and measure 1/4 inch wide x 3/4 inch outside diameter. These wheels are used by many and include a zinc diecast inner race and steel ball bearings.