This half-moon shaped switch assembly is used to control the speeds of the internal digital Leslie found in the XK Pro System, XK5, XK-3, XK-3c, XK-1c, SKX and SK-2 as well as the speeds of any Leslie speaker that is connected to the unit.  This switch assembly mounts to the front rail via the two thumbscrews provided and can easily be removed for transportation purposes.

Hammond CU1 Leslie Control Switch