Abstract: A grease gun plunger of elastic material formed to provide a central hub, a peripheral skirt, and a web joining the skirt to said hub, the web being unitary with said hub at a first end of the plunger and with the skirt at a second end of the plunger to comprise a generally conical partition across the plunger. The skirt has an outer surface which tapers inwardly in both axial directions from a location of maximum outside diameter near the second end of the plunger. The plunger has a peripheral groove around said second end, said groove having a radial dimension substantially equal to the radial thickness of said skirt.