I have had a severe Senior Moment. I cannot recall the name of a common part used in rebuilding the front suspension on most vintage cars.
The item is used to seal out moisture and grit from the king pins and upper and lower pins on a front suspension. They are round steel, cupped disks that you insert into the top and bottom of say, the king pin cylinder, and hit it with a hammer to expand it into the hole, thus sealing it. Some have a threaded hold for a grease fitting.