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 which press-fits into the bottom of the H-Bar. For sliding glass panels fabricated with up to 15 square feet of 1/4" (6 mm) plate glass or other glazing material. For larger panels up to a maximum size of 15 square feet, four each D649 ball bearing steel rollers should be used.