The torque spec for the receiver extension nut (AKA castle nut) is 38 - 42 ft. lbs. You should use some moly grease on both sets of threads as an anti-seize measure and then stake two of the three notches. The spread on the range is in case you don't have two notches presented for staking on the low end of the range. And, as mentioned, no Lock Tite.

