a torque wrench...each side of the hex nut representing a "flat". For -4(1/4") and -5(5/16") fittings after hand tight, tighten two more flats. For -6(3/8") tighten 1+1/4 flat. For -8(1/2") and -10(5/8") tighten one more flat. We use this process everyday with great success. We have used the flaretite adapters for a field fix. They work great.