The 138190035 Rocker Lock Nut for the Non-Hemi Clones and Predators is a jam nut used to prevent the rocker adjuster nut backing off the stud. 

The rocker lock nut prevents the lash from widening too far since the rocker adjuster nut is loose to allow the rocker to pivot. In most cases, the lash will need to be reset after the engine has gone through a heat cycle. 

The Rocker Lock Nuts are the OEM Replacement for 196cc 6.5hp GX200 Clones, including the Tillotson 196R/RS, Ducar 196, and Box Stock 196. These also fit the Predator 212 Non-Hemi Cylinder Heads.

Torque Specs: 85 in/lbs