Hand-tighten snug, then a quarter turn.

Tighten by hand with the wrench until the nut is snug, then give it another quarter turn.

That’s close enough to the 15–25 ft-lbs most saws specify. A torque wrench is overkill here — the bar has to move slightly when you adjust chain tension later anyway. Overtighten and you risk stripping the threads in the housing (plastic or magnesium, neither forgiving). Undertighten and the bar wanders, which throws the chain off and makes you adjust more often.

Just use the L-shaped wrench that came with the saw. It’s designed so you can’t really overdo it by hand. If you’re using a ratchet or a power tool, stop — you’re asking for a broken stud.

Future you has better things to do than helicoil a chainsaw crankcase.