Bolt torque chart

Published 28 September 2026. Last checked 29 September 2026.

What holds a joint together is the preload: the tension in the bolt that clamps the parts. Torque is only the indirect way most people set it. Every chart on this site states the preload first, then the torque that should produce it, with the friction assumption printed in the column heading. All values are computed with the same engine as the bolt torque calculator, and each row opens the calculator with that case loaded.

Which chart to use

Structural bolts are the exception to the torque-chart habit. The RCSC Specification for Structural Joints does not accept a torque from a table for pretensioned or slip-critical joints. The 2025 edition requires turn-of-nut, twist-off tension-control bolts, direct tension indicators or the combined method. The F3125 chart gives torque estimates for planning only.

What the nut factor K means

The short-form relation $T = K\,F\,d$ links torque T, preload F and nominal diameter d through one number, the nut factor K. It is not a friction coefficient. It lumps together thread friction, friction under the head or nut, and the small share of torque that actually stretches the bolt, which is typically only 10 to 15 % of the total. Because friction dominates, the same torque can give very different preloads. At a fixed torque, preload is inversely proportional to K. A bolt torqued to a dry-thread value but assembled with oil can be pushed well past the intended preload.

Source: Budynas and Nisbett, Shigley’s Mechanical Engineering Design, 10th ed., McGraw-Hill, 2015, Table 8-15. Bickford, An Introduction to the Design and Behavior of Bolted Joints, 4th ed., CRC Press, 2008, discusses how widely measured nut factors scatter for nominally identical parts.

The charts use K 0.20 for plain or zinc-plated steel as received and K 0.15 for a lightly oiled fastener. A third column comes from VDI 2230 Part 1:2015. It splits friction into thread and bearing coefficients (both 0.12) and uses the real thread pitch and head bearing diameter. That method is more physical, but it still needs a friction value you believe. Whatever the method, torque control alone typically leaves a preload scatter of about ±25 %. If the preload matters, calibrate the torque with a torque-tension test on the actual parts or use angle or elongation control.

How to read a row

Take M12 class 8.8. Its proof load is 580 MPa times a stress area of 84.27 mm². The chart uses 75 % of it as the preload. At K 0.20:

The same bolt oiled, at K 0.15, needs only 66.0 N·m for the same preload. Tightened to 88.0 N·m oiled, it would reach about 48.9 kN, its full proof load. Match the column to the parts on the bench.

None of the charts consider joint stiffness, embedding or external load. They set the assembly preload only. For the full joint analysis, VDI 2230 Part 1 applies.