Double nut adjustment. Solid center support of blades for stability. Square driver on shank. HSS blades. Blades have hollow ground cutting edge to reduce friction. Ends are center drilled so blades can be sharpened in place.Sizes: 1/4" - 9/32", 9/32" - 5/16", 5/16" - 11/32", 11/32" - 3/8", 3/8" - 13/32", 13/32" - 7/16", 7/16" - 15/32".