Grease fitting

The arrangement is thus essentially a valve that opens under pressure to allow lubricant to pass through a channel and be forced into the voids of the bearing.

The ball excludes dirt and functions as a check valve to prevent grease escaping back out of the fitting.

The ball is almost flush with the surface of the fitting so that it can be wiped clean to reduce the amount of debris carried with the grease into the bearing.

Sometimes a cup was mounted, acting as a small reservoir, which would weep oil slowly or could be turned at regular intervals to inject grease into the fitting.

The standard mode of maintenance was to have each machine's operator, or a dedicated oiler, go around adding a small squirt of oil or blob of grease to each and every hole or cup on a frequent basis.

But locomotives, rail cars, agricultural implements, and automobiles were less certain of good care, and lubrication quality without constant lubing tended to be intermittent, from mediocre to bad.

Since the 1920s, the ever-growing proliferation of sealed bearings throughout the manufacturing industries has made the use of grease fittings less common.

Grease fittings are far from obsolete, however, and much new machinery is built with them every year (e.g., tractors, lawnmowers, industrial plant equipment, and still a few car and truck parts).

Norton Commando motorcycles (1967–1975) had a 'grease' nipple fitted to the swing arm assembly but heavy gear box oil was stipulated by the factory.