This is a slick solution to a common issue found in vintage VW's.  It's common for people to have converted their '66 and earlier Bugs to 12 volts from the original 6 volt system. In many cases, the flywheel has not been changed when doing so.  The 6V flywheel has a different number of teeth (109) than the later 12V one.  So the 6V starter is usually retained in order to keep things simple.  This can cause them to be excessively loud and wear out prematurely, as double the voltage is applied to the starter.

This replacement starter is built with newer technology, uses less current, and is designed to use the full 12 volts, yet still be compatible with the 109 tooth original flywheel.  It's great for replacing the incorrect and non-matching starter that may have burned out already, or for completing your own 12V conversion without having to pull the engine to change the flywheel and clutch to the later style.