Hobson technical document
Nord-Lock Washer Hardness Table and Hardness Conversion Chart
A one-page Nord-Lock data sheet, distributed by Hobson, on why hardness matters for wedge locking washers. It gives the minimum hardness of Nord-Lock steel and stainless washers, explains how to check that the washers are locking, and includes a Vickers, Brinell and Rockwell hardness conversion table.
What this covers
- Why hardness matters
- Checking the locking action
- Nord-Lock hardness table
- Hardness conversion table
Applies to Flat Washer, Mudguard / Penny Washer and Safety / Vibration-Lock Washer.
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- The surfaces the washers clamp against should not be harder than the Nord-Lock washers, or the wedge locking action cannot work.
- Steel washers (through hardened, zinc flake coated), NL3 to NL130: 465 HV1 or harder. Stainless steel washers (surface hardened), NL3ss to NL80ss: 520 HV0.05 or harder.
- To check they are working: tighten the joint, then undo it. The washer pair must slide against each other, you should feel a click as the cams ride over, and the mating surfaces should show clear impression marks.
- The conversion table runs from 300 to 540 HV, for example 400 HV is 380 HB and 40.8 HRC.
- It also marks the ISO 898-1 surface hardness band of each bolt class: up to 375 HV for 8.8, 320 to 390 HV for 10.9 and 385 to 465 HV for 12.9.
Who it helps: Engineers and maintenance staff matching Nord-Lock washers to hardened bolts and mating surfaces.
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