DIN 981 specifies the dimensions and tolerances for bearing lock nuts (km series). The full dimensional table is reproduced below, followed by the DIN, ISO and ASME parts that match or supersede it.
- Standard
- DIN 981
- Product
- Bearing Lock Nuts (KM Series)
- Governing standards
- DIN 981
Equivalence between national standards is dimensional, not always metallurgical. Check the property class separately when substituting.
The table below lists the dimensions catalogued for bearing lock nuts (km series) under DIN 981. The scope of DIN 981 itself is not summarised here — where a figure matters, confirm it against the published document.
DIN 981 — Scope
The table below lists the dimensions catalogued for bearing lock nuts (km series) under DIN 981. The scope of DIN 981 itself is not summarised here — where a figure matters, confirm it against the published document.
Tolerance & Product Grades
Product grade is a concept from dimensional fastener standards and does not apply to DIN 981. Tolerances for this part are the limits shown against each dimension in the table.
Dimensions Specified by DIN 981
| Size | Thread size | Outer diameter D (mm) | Nut height m (mm) | Slot width (mm) | Slot depth (mm) | Matching tab washer | Reference standard |
|---|
| KM0 | M10x0.75 | 18 | 4 | 3 | 2 | MB0 | DIN 981 |
| KM4 | M20x1.0 | 32 | 6 | 4 | 2 | MB4 | DIN 981 |
| KM6 | M30x1.5 | 45 | 7 | 5 | 2 | MB6 | DIN 981 |
| KM8 | M40x1.5 | 58 | 9 | 5 | 2.5 | MB8 | DIN 981 |
| KM10 | M50x1.5 | 70 | 9 | 6 | 2.5 | MB10 | DIN 981 |
| KM12 | M60x2.0 | 80 | 11 | 6 | 3 | MB12 | DIN 981 |
Companion Standards
A complete specification for bearing lock nuts (km series) normally cites several documents: one for the geometry, one for the material or mechanical properties, and one for the finish. DIN 981 is one of them, not all of them.
When to Specify DIN 981
DIN 981 is still widely used in European mechanical engineering and as a cross-reference on legacy drawings; its ISO equivalent is preferred for new designs.
Custom manufacturing · Made to drawing
Need a nut to this standard in a non-standard size?
Parts built to DIN 981 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or tapping.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
Custom nut manufacturingSend a drawing
Applications & Industries
Bearing Lock Nuts are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from KM0 to KM12 (size designation).
Industries that specify Bearing Lock Nuts
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Pumps & electric motors
Shaft-end retention during rebuild.
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Bearing assemblies
Setting and holding bearings on adapter sleeves and threaded seats.
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Gearboxes & spindles
Axial location of shaft-mounted bearings.
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Maintenance & MRO
Replacements matched to the existing bolt class, thread and finish.
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Building services
Threaded rod, channel and suspension assemblies.
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Machine building & OEM
The clamping counter-face on studs and bolts throughout an assembly.
Typical applications
- used with the matching MB tab washer — the nut alone is not locked
- setting a bearing on a tapered or threaded shaft seat
- tightened with a C-spanner or pin wrench into the slots
- joints re-torqued at a service interval
- completing a bolted joint on a stud, rod or bolt
- locking an adjustment so it cannot drift
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Vibration
- Specified where cyclic load would loosen a plain nut or screw — rotating plant, rail, mobile equipment and anything that is not re-torqued in service.
- Match the class
- A nut below the bolt property class strips before the bolt reaches its own limit — pair class 8 nuts with 8.8 bolts, class 10 with 10.9.
Full application guide: where Bearing Lock Nuts are used, how to specify them, and the cases they are wrong for
