The center is made of alloy steel and is waterproof design. Concentricity tolerance is 0.005mm(2-1/2"~8")/0.006mm(10"~12");roundness is 8") 0.006mm(10"~12"). The center isassembled with ball bearing and tapered roller bearing. Bearing is from Japan BAND Weight of working piece in load/kgs MAX /500KG.