Whiteside W300 15 Pc. Shim Washer Kit is designed to provide precise adjustments in the spacing of any router bit assembly with a 5/16" diameter arbor. This versatile kit is i for use with slot cutters, stile and rail sets, window sash bits, and tongue and groove bits. The 15-piece set includes three washers each of five different thicknesses: .004", .006", .008", .010", and .012". Each washer measures 5/16" ID by 1/2" OD, ensuring compatibility and ease of use. Manufactured by Whiteside Machine Company in Claremont, North Carolina, this kit quality and reliability for fine-tuning your woodworking projects. Model Number: W300