High-speed ball-bearings produced especially for XRAY. ID x OD x thickness (") = 1/4" x 3/8" x 1/8". Group of 2 pieces. Top-quality expert ball-bearings for super-free, super-smooth operation. These best quality ball-bearings are degreased and gently oiled with AeroShell Fluid 12 oil for optimum smoothness, endurance, highest tolerance and optimum performance.