Metal spacer is used on slitter shaft to adjust different distance between slitting knife according to needed width of coiling strips. Same high pricision as slitting knife's; Reasonable price, not as expensive as knife of raw material; Wear resistance, but lighter for machine shaft to ensure higher precision of slitting strip and easier assembling. Details: Material of separator 9CrSi / 52100/ SKD11 Thickness tolerance ±0.00008" Hardness 45-56HRC outside diameter tolerance ±0.001" parallelism within 0.0001" flatness within 0.0001" concentricity within 0.001" max surface roughness Ra0.2