Sold new on Bolduc, their product description: "A uniquely designed fixture that allows you to cut perfect slots for shims or small planks using an air grinder and a specially made carbide bit. This allows you to turn wandering or branched cracks into perfectly machined grooves that will accept one of our three sizes of Bolduc shims #3320, depending on the depth of cut. It can also be used to remove planks that have multiple cracks close together where shims won't work and wider planks would be fitted."