- a tool for enlarging a drilled hole for a portion of its length, as to permit sinking a screw head.
- the portion of the hole so enlarged.
- to enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.
Origin of counterbore
Examples from the Web for counterbore
Historical Examples of counterbore
If taken off at all it must be pulled, for the dowel-pins, key and counterbore are close fits.Steam Turbines
Hubert E. Collins
For enlarging a hole for a certain distance the counterbore is employed.
A counterbore in the arbor hub provides clearance for the hub of the pulley which projects beyond the rim on one side.Turning and Boring
Franklin D. Jones
For counterboring small holes or for facing the metal around their ends, the form of counterbore shown in Fig. 1746 is employed.
That it may always do this and yet leave sufficient clearance, the counterbore has been devised.Farm Engines and How to Run Them
James H. Stephenson