Urgh Factor 1.
Not an exact measurement, but a useful one.
Urgh Factor = spin the nuts tight as they will go without significant effort, and then each 1/4 turn that requires any actual effort to make is an "Urgh!" factor.
(So Urgh-factor 4 would be one complete revolution.)
While it's not exact, it's a right useful way to measure torque if you don't have a torque wrench, silly as it sounds.
Head nuts should be firmly tight, but not gorilla-armed in, cause if you strip the bottom threads of the rods outta the transmission casing, you're majorly screwed.