If taken off at all it must be pulled, for the dowel-pins, key and counterbore are close fits.
A counterbore in the arbor hub provides clearance for the hub of the pulley which projects beyond the rim on one side.
For enlarging a hole for a certain distance the counterbore is employed.
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.
The jaw end is counterbored out with a 45-degree counterbore to form a bearing for the forward end of the micrometer screw.