The Shepherd PSD50223BK-U swivel caster features 1.9685" urethane twin wheels and a 7/16" x 7/8" Grip Ring, capable of a 75 lb. capacity per caster. Complete caster specifications and downloadable CAD model are provided below. Model PSD50223BK-U brakes without weight, rolls when weight is applied; 12-15 lbs to release the brake. Constructed of injection-molded engineering-grade nylon and floor-protective polyurethane wheel treads, Shepherd Self-Braking Chair casters are designed to make replacing your standard chair casters a breeze. Self-Braking Chair casters utilize weight (or the lack thereof) to initiate or release the integrated friction brake.