This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The plug of a worn stop cock, or one that has been reground, of the type shown in the illustration will project
Removing a Portion of the Plug and Shortening the Screw Allows the Parts to be Drawn Tightly Together
beyond the bottom so that the ring, or washer, and screw will not draw it tightly into place.
To remedy this trouble, file off a portion of the plug on the line AA and also file off a sufficient amount of the screw on the line BB. When the plug is replaced and the washer and screw drawn up, the stop cock will be as good as a new one. - Contributed by James M. Kane, Doylestown, Pa.