I asked IPd since I bought the plugs from them.... They told me the torque on my 2001 S60 should be 30 nm.... If you don't have a torque wrench, then finger tighten the plug with your ratchet till you feel strong resistence, then give it a final quarter turn... be especially careful not to cross thread the plug when installing! Hope this will help others who didn't know.

 

Also...don't forget to put a small amount of anti seize lube on the plug threads so next time you need to remove them, it won't be that much of an effort. Another trick is to also use a piece of latex air hose tubing from an auarium pump (which I already had) & attach it to the top pole of the spark plug then lower the plug into the engine block. Slowly turn the tubing clockwise to screw the plug in. You will notice if the plug was threaded correctly or not. Once you have threaded it correctly, pull out the latex tube & complete the install....