Two flute straight cutters produce a cleaner finish than the single flute cutters & are suitable for grooving, rebating, mortising & drilling. Use High Speed tooling when working with softwoods such as Pine. H.S.S Tooling. 1/4 in. Shank. C = 28 mm. D = 6.3 mm. 1/4 in. Two flute straight cutters produce a cleaner finish than the single flute cutters & are suitable for grooving, rebating, mortising & drilling. Use High Speed tooling when working with softwoods such as Pine. H.S.S Tooling 1/4 in. Shank. C = 28 mm. D = 6.3 mm. 1/4 in.