Turn-of-nut method: rotation table and procedure (RCSC 2020)

Nut rotation from snug-tight (RCSC Table 8.1)

Nut rotation is relative to the bolt, whichever element (nut or bolt) is turned. Tolerance +60 deg (1/6 turn), -0 deg. Applies only to joints in which all material within the grip is steel. Bolt length > 12db: determine rotation by testing in a bolt tension measurement device. Beveled washer not used (sloped faces).⁠¹

Why turn-of-nut works

Turn-of-nut controls strain, not torque. Once the plies are in firm contact, a set nut rotation stretches the bolt into its inelastic range. RCSC’s commentary calls this “inherently more reliable” than a method that depends entirely on torque ⁠¹. Mean installed pretension is about 1.35 times the specified minimum for A325 bolts and 1.26 times for A490 ⁠¹, against 1.13 for the calibrated wrench ⁠¹.

It only works if two things hold: the joint is fully compacted before the turn, and the unturned part does not rotate while you turn the other ⁠¹.

Procedure

1. Check the bolts first

   Pre-installation verification is required for turn-of-nut too. Snug at least three assemblies of each diameter, length, grade and lot in a bolt tension measurement device, match-mark, apply the Table 8.1 rotation and confirm they reach the Table 7.1 tension (29 kips for a 3/4 in A325) ⁠¹. If a bolt is too short for the device, install it in a steel plate, apply the turns, then remove it to confirm it did not strip ⁠¹.

2. Snug-tighten the whole joint

   Put bolts in all holes, then work from the most rigid part of the joint outward. Snug-tight means a few impacts of an impact wrench, or the full effort of an ironworker on an ordinary spud wrench, with the plies in firm contact ⁠¹. More than one pass may be needed ⁠¹.

3. Match-mark

   Mark across the nut and the protruding bolt end after snugging. RCSC does not require it, but notes it helps installation and inspection ⁠¹. With match-marks the inspector can check the turns visually afterwards instead of watching the work ⁠¹.

4. Apply the rotation

   Turn the nut (or the head) by the Table 8.1 amount, again starting from the most rigid part ⁠¹. Hold the other element so it does not rotate ⁠¹.

5. Do not back off

   After pretensioning, turning the nut or head in the loosening direction is only allowed for complete removal of the assembly ⁠¹.

Reading the table

Rotation is counted relative to the bolt, whichever part is turned. Bolt length is measured in bolt diameters (db). A 3/4 in bolt 3 in long is 4db, so it takes 1/3 turn with both faces square; at 3-1/4 in it is over 4db and takes 1/2 turn. “Sloped” means an outer face up to 1:20 off square with no beveled washer ⁠¹.

The tolerance is plus 60° (1/6 turn) and minus 0° for every rotation ⁠¹. RCSC 2020 lists “revised tolerance for turn-of-nut (Table 8.1)” among its changes ⁠¹, so tolerances quoted from earlier editions are out of date. Over-rotation is not a reason to reject a bolt ⁠¹. In tests of 7/8 in bolts 5-1/2 in long, set at 1/2 turn, A325 bolts did not fail until about 1-3/4 turns past snug and A490 about 1-1/4 turns ⁠¹. Still, RCSC says to avoid deliberate over-rotation, because soft nuts can strip and hardened nuts can crack ⁠¹.

Limits

• Steel grips only. Table 8.1 applies only when all material in the grip is steel ⁠¹.
• Over 12 diameters. No research sets the rotation. Test three samples in a bolt tension device, find the rotation from snug to the Table 7.1 tension, and round up to the next 1/6 turn (270° becomes 5/6 turn). If that comes out less than the Table 8.1 value for 12db, use the 12db value ⁠¹.
• Galvanized or coated bolts. Very effective lubricants have let a spud-wrench snug alone reach full pretension. Dry or poorly overtapped galvanized nuts can seize and twist the bolt off below pretension. The verification test shows which case you have ⁠¹.
• No DTIs for verification. A DTI cannot serve as the tension device for turn-of-nut, because crushing it uses up part of the rotation ⁠¹.

Old table numbers

Some study guides and bolt FAQs still cite “RCSC Table 8.2” for turn-of-nut. In the 2020 edition, Table 8.1 is the turn-of-nut rotation table, Table 8.2 is the combined method, and the old “Table 8.1 Minimum Bolt Pretension” is now Table 5.2 ⁠¹.

The combined method

Added in RCSC 2020, the combined method applies an initial torque, then a set rotation ⁠¹:

• Initial torque. Use the supplier’s value. If none is given, use RCSC Table 7.3: for a 3/4 in bolt, 170–205 ft-lb (230–278 N·m) for Group 120 and 210–250 ft-lb (285–339 N·m) for Group 150. For a 1 in bolt, 405–480 ft-lb (549–651 N·m) and 510–605 ft-lb (691–820 N·m) ⁠¹. The tool output must not vary by more than ±10% ⁠¹. Table 7.3 must not be used in place of supplier torque values ⁠¹.
• Initial tension check. That torque must give at least the Table 7.2 initial tension, which is 0.45 times the minimum pretension: 13 kips for a 3/4 in Group 120 bolt ⁠¹.
• Rotation. Then turn 90° for bolts up to 4db or 120° for 4db to 8db, tolerance +45°/−0° (Table 8.2). Bolts over 8db need testing ⁠¹.

Table 7.3 holds the only torque numbers in the Specification, and they are initial torques, not final installation torques. Combined-method assemblies are treated as matched assemblies, may be relubricated only by the manufacturer, and need an F436 washer under the nut ⁠¹. Tools must be rechecked at least weekly ⁠¹.

Sources

1. 1
   Research Council on Structural Connections, RCSC Specification for Structural Joints Using High-Strength Bolts, June 11, 2020Checked 21 Oct 2026

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