Drill America Counterbore, Aircraft Series, 19/32" Size, 1/8" Pilot Hole, 1/4" Shank, 2-13/16" OAL

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 the hole is enlarged to a considerable depth, it is designated as counterboring.