Combination of a steel concave or grooved ball bearing roller that is 5/16 inches thick with a 1/4 inch axle hole and a combination of 5 different axle choices. Depending on the situation, you can choose to rivet the roller into place or use a roll pin, drive pin, binder post and screw or bolt and nut. Regardless of how you need to install the new roller into your existing roller housing, in most cases, one of the five choices will work.