Wheelchairs, Mobility Scooters and Accessories MJM International R-3TW-RP Replacement Caster Set, 3″ (Pack of 4) Review Posted on June 11, 2018November 7, 2018Author Marauderby Product Description Replacement 4″ twin nylon threaded stem casters / set 2-lock 2-nonlock. Manufacturer Contact Information 800-270-6199