This Agilent Varian OEM TriScroll 300 and 600 spieth locknut is used to set the depth of the orbiting scroll plate assembly. The orbiting scroll plate assembly must be set to the correct depth on the crankshaft using a depth gauge. The locknut is secured to the crankshaft using a special locknut spanner wrench, and locked in place by the included four M4x12 socket head cap screws.