Use with Super Erecta posts and shelves to create a mobile shelving unit to meet your special needs.,Stem casters are shipped with donut bumper at no additional charge.,5" diameter polyurethane,flat wheel tread with 1.25" face,finish:Heavy Gauge Cold Rolled Steel Nickel Plated Horn. Polyurethane Flat Tread. Polyethylene Hub.;color: Silver/Gray