Designed to reduce the Arbor. Most saw blade bushings have serrations on the outside diameter edge to provide a better grip and fit, #BU-200, (D) diameter: 1, (D) bore: 3/4, kerf (B): .075 (1.9mm), a: .075 (1.9mm), BU-200 High precision saw blade bore reduction Bushing 1 inch to 3/4