In 1997 the old pointer style lock that adjusts backlash on the mill X- and Y-axis leadscrews was replaced with a star gear type lock to make adjustment easier. With the advent of CNC (Computer control) there has been an increased demand for reduced backlash settings. To serve this purpose, the size of the teeth on the star gear have been reduced to give a tighter fit and remove play from the backlash nut.
All new Sherline machines after 6/04 include these revised star gear backlash nuts and locks, but they can be retrofitted to any Sherline mills made after 1997 when the old pointer lock system was phased out. It will not replace the pointer system as the hole centers for the lock are different.