The washer at the base of the new plug threads is a crush ring. As you tighten you will feel the plug seat on the crush ring/washer and with a half turn of tightening you will feel the washer "crush". Stop. You're done. No need for a torque wrench. This only applies on fresh plugs, once the washer is crushed its crushed. If you don't have compressed air use a rag and small screwdriver to clean around the base of the plug before you take it out.
