A chalk mark or paint is then made on the bolt and nut. The bolt is tightened further by either hammering on the spud wrench or using a pneumatic impact wrench until the rotating part has rotated the required amount. The paint or chalk mark shows how far the part has rotated and the rotation is always measured relative to the rotation of the bolt. The number of turns past snug is dependent on the length of the bolt relative to its diameter and the geometry of the two surfaces. The previous table shows the number of rotations for a variety of bolt lengths for flat horizontal surfaces.
Most iron workers use pneumatic power wrenches, also called impact wrenches, to tighten bolts.
Calibrated wrenches can be set to stall at a specified torque thereby achieving the correct amount of bolt tension. Unfortunately, calibrated wrenches need to be calibrated at least every day since they tend to lose their calibration relatively quickly. An indirect way to verify that a bolt has been properly tightened is to use tension indicating bolts like the one shown at the right. When the bolt is tightened to the proper load, the right end of the bolt shank snaps off. An ironworker would simply keep tightening the bolt until the tip breaks off and an inspector could easily verify that the bolt was properly tighten by ensuring that the tip is missing.