These CRL Heavy-Duty Ball Bearing Wheel Assemblies are used in our Custom Showcases with sliding rear doors with D610, D615, LK610, KK610, and MC610 H-Bars This ball-bearing roller unit is fabricated in a stamped steel housing that press-fits into the bottom of the H-Bar For sliding glass panels fabricated with up to 15 square feet of 1/4 (63 mm) plate glass or other glazing material For larger panels up to a maximum size of 15 square feet, four D649 ball-bearing steel rollers should be used