21/64" X 3/32" Pilot Hole HSS Straight Shank Counterbore DEWCBR21/64

Size: 21/64, Material: High Speed Steel, Finish: Uncoated (Bright), Overall Length: 3-13/16, Shank Size: 5/16, Shank Type: Round Counterboring is the enlargement of a portion of a hole that has previously been formed. If the counterbored portion is shallow (1/8" or less), the operations is usually known as spot-facing; for example, a flat seat for a bolt head or nut. If, on the other hand, the hole is enlarged to a considerable depth, it is designated as counterboring. These counterbores are made of two-piece construction, having an integral shank and counterbore-cutter, and a pilot that is interchangable, which provides flexibility in the use of the tool.