Grinding stone holders with stones connects power trowels to floor grinders. Each holder bolts the blade arm with #6 grit stone (SK320). Stones can be rotated for even wear. Steel construction Rotate stone for even wear Includes #6 Grit grinding stone (SK320). Fits machines smaller than 36 In. Stone is replaceable Made in the USAStone is replaceable. (4-PK) They are proudly made in the USA.