A jam nut is a thin locking nut — roughly 30–50% thinner than a standard hex nut of the same thread — threaded onto a rod end’s shank and tightened against a tube adapter or bung to lock the rod end’s length and prevent it from unthreading under vibration. Because a jam nut has fewer engaged threads than a standard nut, it’s typically torqued to only a third to two-thirds of a standard nut’s torque spec, and the “turn-of-the-nut” tightening method is often preferred over a fixed torque number.
See the full guide: Rod End & Heim Joint Torque Specs: Complete Guide