Turn-of-the-Nut Method of Tightening Bolts

Written by phillip woolgar
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Turn-of-the-Nut Method of Tightening Bolts
Bolt tightening requires a wrench. (wrench image by Edsweb from Fotolia.com)

Turn-of-nut installation is a standard of structural bolt installation recognised by the Research Council on Structural Connections. Installations that require slip-critical or pretensioned joints, as well as hex head structural bolts, generally utilise the turn-of-nut installation. The method aims at resulting in better uniform bolt pretensions than other forms of torque control. By using the method, there are no calibration concerns and torque wrenches aren't needed. Essentially, turn-of-nut installation simply involves a wrench, screw, washer and nut. Construction companies, however, take testing turn-of-nut installation seriously, because their entire business depends on their construction project not falling down.

Skill level:

Things you need

  • Wrench
  • Bolts
  • Washers
  • Nuts

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  1. 1

    Verify your bolts by taking three of various diameters, lengths, production lot and grade, along with three washers of different diameter and production lot, and three nuts with different grades and production lots. Assemble the first set in a Skidmore-Wilhelm, the construction industry's standard bolt testing machine.

  2. 2

    Tighten the bolts into the joint with a wrench to the Skidmore faceplate. Tightening requires about a one-third turn for bolts under five inches. Two-third turns are usually required for bolts between five and 16.5 inches.

  3. 3

    Line up the washer and nut at the other side of the bolt and secure with your wrench.

  4. 4

    Confirm on the Skidmore dial gauge that the tension is at least five per cent above the minimum bolt pretension. Half-inch bolts have a 12.5 kips, a unit force that equals 454 Kilogram. Five-eighths of an inch have a kips of 20. Various sizes of bolts require different kips.

  5. 5

    Log the tension in a log book and remove the assembly.

  6. 6

    Use the same method on whatever bolt you want to tighten.

Tips and warnings

  • Note that the utilisation of the Skidmore-Wilhelm is a standard followed by construction companies. It is a requirement so those companies can be ensured of the structural integrity of whatever they are building. Most household projects don't utilise the testing procedure. Construction companies, however, take the aforementioned steps very seriously.

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