Well, yes, typically a torque wrench. The manual should have the torque spec. Also, they are tightened a criss-cross pattern so the head gets tightened down evenly. It should also be done in 3 passes. For example, if the torque spec is 40 ft/lbs, I'd do the 1st pass at say 20, the next a 30, then the final at 40. It's more critical they they are all tightened evenly to each other than to hit the number exactly. Uneven torque may lead to warpage when exposed to multiple heating/cooling cycles. That's why I suggested that you check the head for warpage. All's that's needed is a piece of modern glass (float glass) and a feeler gauge. The manual will give a spec. on the maximum warpage amount. Select a feeler gauge that matches that amount. Place the head on the glass and try to slip it under the head. If it will slip between the head and the glass, it's warped excessively and should be replaced.