This answer is in the link that Dan postedAnyone know the tap I would need to retap glow plug threads? What size and thread tap is it?
That (35 Nm for my GP) by the way is the "failure moment" or the maximum. I set my torque wrench lower to be on the safe side.There is a head in the shop right now that has two glow plugs that are not cooperating. When using the recommended 25 ftlbs of torque at first one would budge and one would not. After two days of soaking with KROIL, one will turn about 1.5 turns the other about .5 turns before they reach 25 ft*lbs.