Spool Serrated Top Pins

A standard top pin is a plain cylinder. A spool is waisted and a serrated pin is ridged, and both are shaped so that the plug binds and gives false feedback when it is being picked rather than turning smoothly to the shear line.

They fit the same chambers as standard pins, so a cylinder can be upgraded during a normal rekey. Mixing a few through the stack is more effective than filling every chamber, and it keeps the lock pleasant to use.