This is a combination of a 1-1/2 in. diameter nylon concave or grooved ball bearing roller that is 5/16 in. thick with a 1/4 in. axle hole and a combination of 5 different axle choices. Depending on the application, 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.