Counterbore
From Wikipedia, the free encyclopedia
A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole, or the tool used to create that feature. It is usually used when a bolt or cap head screw is required to sit flush with or below the level of a workpiece's surface (By comparison, a countersink makes a conical hole and is used to seat a flathead screw).
The uppermost counterbores shown in the image are the same tool. The smaller top item is an insert, the middle shows another three-fluted counterbore insert, assembled in the holder. The shank of this holder is a morse taper although there are other machine tapers that are used in the industry.
The lower image is of a plain counter bore designed to fit into drill chuck, and being smaller, is economical to make as one piece.
 Metalworking:
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Broach | Burr | Chisel | Counterbore | Countersink | Cutting tool | End mill | Metalwork file | File | Hand scraper | High speed steel | Milling cutter | Reamer | Stellite | Tipped tool | Tool bit |
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