When coupling a drawbar (ball-and-cup) connection, after reinstalling the safety lock screw and self-locking nut, to what torque should they be tightened?

AAMVA CDL Manual, Section 6.4.5, Step 4, p. 6-11

A drawbar coupling carries the full pulling and braking load between a tow vehicle and trailer, so an under-torqued lock screw can work loose over the road, while mis-torquing in either direction risks a coupling failure. The 350-400 Nm spec gives drivers and mechanics a precise, checkable number rather than a guess.