Rubber cushion (or foot) to protect your table top.
I have lots of class participants who tell me their machines don't have bed cushions. They look at where the bed cushions should be and all they see is a glob of gray goo. At one time their machines had bed cushions or 'feet' that looked like the one in the picture, but time, rot, air pollution, etc. have deteriorated the rubber.
The old cushion can be removed by digging it out with an old screwdriver after softening with kerosene. Once you get enough of the old cushion out to see the screw, remove the screw to replace the old cushion with one of these great new ones. Replace all four (sold as a set of four), so your machine stays level. Class participants in the Nova's Featherweight Maintenance Workshop learn this as well as other handy skills.