The diagram shows the plug but not the wick.
Look on the next page under "Care and Adjustment".
"Place a drop or two of oil on the felt wick in the distributor cam, tighten the grease cup a turn every 1,000 miles... "
I think the plug in this example is serving as a seat between the wick and spring.
By definition, a wick's purpose is to convey liquid (lube) by capillary action. Tightening the grease cup is like pumping pressure in a kerosene lantern.
I understand the principle now. I don't have a wick or plug in my unit but I'll take care of that.
This has certainly been informative!
Jerry
