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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 operation 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 interchangeable, which provides flexibility in the use of the tool.