Nord-Lock Washer Torque Chart.

The most common question about fitting Nord-Lock washers is what they do to the tightening torque. The answer is simpler than most people expect: nothing. A Nord-Lock washer locks the joint with tension rather than friction, so the bolt is still tightened to the standard torque for its size and property class. There is no torque penalty to add and no prevailing torque to overcome, unlike a nylon insert nut or a thread locking patch.

This page brings the numbers together in one place. Use the Nord-Lock torque chart below to find the tightening torque for your bolt size and grade, then follow the tightening procedure to make sure the wedge lock seats properly. The chart covers metric coarse threads from M3 to M42 across property classes 8.8, 10.9 and 12.9, which spans the standard Nord-Lock washer range.

Contents:

• Do Nord-Lock Washers Change the Tightening Torque?
• Nord-Lock Washer Torque Chart, Metric Coarse
• How to Tighten a Joint Fitted With Nord-Lock Washers
• FAQs

Do Nord-Lock Washers Change the Tightening Torque?

No. The wedge-locking action does not rely on friction between the washer faces, so it does not consume any part of the applied torque and does not require the bolt to be over-tightened to work. Torque the fastener to the figure specified for the bolt itself and the cams will engage as the joint comes up to preload.

This is the practical advantage of a tension-based locking system. A friction-based device has to be tightened past its own resistance before it starts clamping the joint, which makes the relationship between applied torque and achieved preload harder to predict. With Nord-Lock washers, the torque you apply does the job you intended it to do and the locking function is a consequence of the geometry rather than of extra tightening.

Two things do change and both are about the joint rather than the torque. The captive pair adds thickness to the stack, so check the grip length of the bolt still leaves enough thread engagement. The radial serrations also need a bearing surface they can bite into, so the mating face must be sound and softer than the hardened washer face.

Nord-Lock Washer Torque Chart, Metric Coarse

The Nord-Lock torque table below gives recommended tightening torques in newton metres (Nm) for metric coarse threads, calculated for a total friction coefficient of 0.14 at 90 per cent utilisation of the bolt's yield strength. These are the standard figures for the bolt grade, which is exactly what a joint fitted with Nord-Lock washers should be tightened to.

Treat these as guideline Nord-Lock torque specs for a standard joint. Where a joint has been designed to a specific preload, or where the bolt manufacturer publishes its own figure, that figure takes precedence over any general chart, so be sure to double-check and verify before proceeding.

Metric Fine Threads

A fine pitch thread reaches the same preload at a slightly higher torque than the coarse thread of the same nominal diameter, because more of the applied torque is converted into axial load. Where a joint uses a fine pitch bolt, work from the bolt manufacturer's figure for that thread rather than reading across from the coarse column above.

Stainless Steel Bolts

Nord-Lock washers in Stainless Steel - (316L) and Stainless Steel - (254) are commonly paired with stainless fasteners, and for torque purposes an A4-80 bolt behaves broadly like a class 8.8 bolt, so the 8.8 column is the right starting point. Stainless threads are prone to galling under load, so lubricate the thread and the bearing face before tightening and note that doing so lowers the torque needed to reach a given preload. A dry stainless joint tightened to a dry torque figure can seize before it reaches the intended clamp load.

How to Tighten a Joint Fitted With Nord-Lock Washers

• Check the joint surfaces: The bearing faces must be clean, flat and sound. Uneven or painted surfaces stop the serrations biting, and soft surfaces let them embed rather than grip.

• Fit the washers cam face to cam face: The pair goes under the bolt head or nut with the toothed faces outward, against the fastener and the joint. Fitting a pair the wrong way round leaves the joint unsecured.

• Tighten to the standard torque for the bolt: Take the figure from the Nord-Lock torque chart above or from the bolt manufacturer's data. No allowance is added for the washers.

• Tighten in a controlled sequence: On multi-bolt joints, work round the pattern in stages rather than pulling each fastener up in one pass, so the load spreads evenly and the washers all seat.

• Check the joint after initial service: On new assemblies, a first inspection after the joint has been loaded will confirm the washers have bedded in and the preload has held.

FAQs

Q: What is the tightening torque for a Nord-Lock washer?

A: There is no separate torque for the washer. Tighten the bolt to the standard torque for its size and property class, which you can read from the Nord-Lock torque chart above. The washers lock the joint through their cam geometry rather than through added friction, so they need no torque allowance.

Q: Do Nord-Lock washers need more torque than a plain washer? 

A: No. The wedge lock is a tension-based system, so the same torque that produces the correct preload with a plain washer produces it with a Nord-Lock washer. Over-tightening to try to improve the locking effect risks yielding the bolt without adding security.

Q: Where do I find Nord-Lock torque specs for my bolt grade? 

A: The table above covers classes 8.8, 10.9 and 12.9 for metric coarse threads from M3 to M42. For stainless fasteners, start from the 8.8 column and lubricate the thread. For anything designed to a specific preload, use the joint designer's or bolt manufacturer's figure.

Q: Should Nord-Lock washers be re-torqued in service? 

A: A joint secured with Nord-Lock washers should not lose preload to vibration, so routine re-torquing is not needed to maintain the lock. An inspection after the assembly has first been loaded is still good practice, as it confirms the washers have seated and nothing has settled elsewhere in the stack.

Q: Does the washer change how much torque I need to remove the bolt? 

A: Removal torque is higher than a plain washer joint, because the cams have to be driven back down as the fastener turns. Use a spanner or socket on the fastener as normal and expect a firm initial break, which is the wedge releasing rather than a seized thread.

Q: Can I use a torque wrench with Nord-Lock washers? 

A: Yes. Standard tooling and standard torque control are all that is required, which is one of the reasons the system is straightforward to specify on a production line.