Dormer HSS Bright/ST with Square Hand Reamer B DIN 206, size 21.0. Left hand spiral flute, right hand cut. Widely used by hand for the final sizing of drilled holes. The square on the shank allows it to be held in a tap wrench or a vise depending on whether it is the reamer or the part that is rotating. A long starting taper allows for ease of entry and accurate alignment.