It's a grease cup. Unscrew the cap and you'll find grease in it (maybe). How they work is you pack the cap full of grease and screw it on, which pushes the grease into the bushing in the distributor. Every 6 months or so, give it a turn to keep the bushing lubed.

Last edited by klhansen; 11/16/2018 6:54 AM.
Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.