Premium ceramic and zirconia alumina abrasive blend for excellent performance and efficiencies on stainless steel applications^Type 27 flat face style, with a plastic back is more forgiving than type 29, producing smooth finishes^Plastic back wears away with the abrasive for longer life^4-1/2" and 7" are also available with 5/8"-11 hub for quick disc changes/less downtime^4" with 5/8" hole support increasing volume of 6" tools