The Roller Bearing 'V' Blocks are accurately assemble and precision ground on the bottom taces. Four high precision ball bearing on the top. Thus, providing self aligning wearing hard accurate supports which will not damage even the most delicate work piece. "Crystal" Roller Bearing 'V' Blocks are very useful in tool room, machine shop, assembly, inspeciton, for checking and marking odd shapes jobs, crank-shafts etc.