Apart from the screwdriver slot, the external hexagon, as on bolts, nuts and other components, is the most common means of effective tightening and loosening. Yet, of course, it cannot meet all requirements and alternative means to the same end are pin holes, multiple slots and sockets, which add nothing to the length or bulkiness of components and, in some cases, are more easily produced than hexagons. For grinding in a cone or poppet valve, two holes may be provided in the head for a pin tool as an alternative to a slot requiring milling with a circular cutter. On a large screwed flush-fitting plug two holes, again drilled in the face, provide a means for tightening or loosening with a pin spanner. Round the outside of a gland nut six or eight shallow radial holes admit a shaped pin spanner; and the same number of longitudinal slots take the usual 'C spanner. Two or four slots are usual on locking rings or thin nuts for such parts as cycle freewheels and camera lenses.
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