High-speed ball-bearings manufactured particularly for XRAY. ID x OD x thickness (") = 1/4" x 3/8" x 1/8". Group of 2 pieces. Top-quality professional ball-bearings for super-free, super-smooth operation. These finest quality ball-bearings are degreased and lightly oiled with AeroShell Fluid 12 oil for maximum smoothness, endurance, highest tolerance and maximum performance.