3/8-24 Grade 8 nut- - - - -don't bother with any sort of locking device. Torque keeps rod nuts tight- - - -not some kind of Mickey Mouse plastic lock ring, Pal Nut, or cotter pin. If you're determined to get obsessive-compulsive about it, use a drop of red LocTite. Heat the nut to 500+ degrees F. if you ever need to take it apart again. That's how we built our 700+ HP small block V8s that ran 7K RPM or more twice a lap.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!