Wiktionary
grease nipple
n. A fitting fixed to a piece of machinery, used as an inlet for lubricate grease by means of a grease gun.
Usage examples of "grease nipple".
Bozo's been down on the train to tune the old bomb and it's in the best possible working order, oil changed, every grease nipple examined and greased, spark plugs checked, carburettor and petrol pump cleaned, radiator hose inspected for leaks.