Property Class 12.9 Steel Left-Hand Thread Hex Bolts are supplied to ISO 898-1 property class 12.9. Corrosion behaviour is requires plating or black-oxide protection, the material is magnetic, and the usable service range is commonly limited to approx. +300 °C; confirm against the coating and the load. In practice this grade is the highest common strength class, for high-load machine assembly.
- Grade
- ISO 898-1 property class 12.9
- Corrosion resistance
- Requires plating or black-oxide protection
- Magnetic response
- Magnetic
- Service temperature
- commonly limited to approx. +300 °C; confirm against the coating and the load
Property values are typical for the grade. Certified mechanical test data is available on request for production orders.
For left-hand thread hex bolts in Property Class 12.9 Steel, the controlling selection factors are corrosion exposure, strength requirement and service temperature. The grade data for Property Class 12.9 Steel (ISO 898-1 property class 12.9) is summarized below together with every size supplied.
Why Choose Property Class 12.9 Steel for Left-Hand Thread Hex Bolts
The highest common strength class, for high-load machine assembly. For left-hand thread hex bolts, this matters when requires plating or black-oxide protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 12.9 |
|---|
| Magnetic response | Magnetic |
|---|
| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
|---|
| Corrosion characteristic | Requires plating or black-oxide protection |
|---|
Corrosion Behavior in Service
Carbon and alloy steel left-hand thread hex bolts require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Galvanic & Galling Considerations
For left-hand thread hex bolts in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Sizes of Left-Hand Thread Hex Bolts Available in Property Class 12.9 Steel
| Thread size | Pitch (mm) | Across flats s (mm) | Across corners e (mm) | Head height k (mm) | Thread direction | Common length range (mm) | Reference standard |
|---|
| M6 | 1.0 | 10 | 11.05 | 4.0 | Left-hand | 10~60 | DIN 933 LH |
| M8 | 1.25 | 13 | 14.38 | 5.3 | Left-hand | 12~80 | DIN 933 LH |
| M10 | 1.5 | 17 | 18.90 | 6.4 | Left-hand | 16~100 | DIN 933 LH |
| M12 | 1.75 | 19 | 21.10 | 7.5 | Left-hand | 20~120 | DIN 933 LH |
| M16 | 2.0 | 24 | 26.75 | 10.0 | Left-hand | 25~150 | DIN 933 LH |
| M20 | 2.5 | 30 | 33.53 | 12.5 | Left-hand | 30~150 | DIN 933 LH |
| M24 | 3.0 | 36 | 39.98 | 15.0 | Left-hand | 40~150 | DIN 933 LH |
Dimensions are independent of the material: every size above is available in Property Class 12.9 Steel.
Custom manufacturing · Made to drawing
Need this bolt in a grade that is not listed?
Grade 12 9 Steel is one of the grades the catalog describes. Head form and drive can be specified to the assembly rather than to a standard: a larger bearing face, a security drive, or a socket sized for the tool already on the bench. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
Custom bolt manufacturingSend a drawing
Applications & Industries
Left-Hand Thread Hex Bolts are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from M6 to M24.
Industries that specify Left-Hand Thread Hex Bolts
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Automotive & transport
Chassis, driveline and body fixings that see vibration and are assembled to a controlled preload.
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Steel fabrication
Bolted connections in frames, enclosures, walkways and weldments, on the bench and on site.
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Energy & infrastructure
Tower, pipework, switchgear and plant fixings specified for long service life and inspectable joints.
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Maintenance & MRO
Stocked replacements matched to an existing property class, thread and finish.
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Food, pharma & cleanroom
Stainless assemblies that are washed down, where the finish matters as much as the strength.
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Machine building & OEM
The default fastener on production equipment: covers, brackets, motor mounts and sub-assemblies tightened to a specified torque.
Typical applications
- joints where the property class is stated on the drawing
- clamping two machined faces to a calculated preload
- bolting brackets, motors and gearboxes to a frame
- assemblies that are dismantled for service and re-torqued
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.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where Left-Hand Thread Hex Bolts are used, how to specify them, and the cases they are wrong for
