Property Class 12.9 Steel Fine-Thread Socket Head Cap Screws 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.
Property Class 12.9 Steel Fine-Thread Socket Head Cap Screws combine the dimensional form of DIN 912 / ISO 4762 and ASME B18.3 (UNF) with the material properties of grade ISO 898-1 property class 12.9: requires plating or black-oxide protection, magnetic, service range commonly limited to approx. +300 °C; confirm against the coating and the load. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose Property Class 12.9 Steel for Fine-Thread Socket Head Cap Screws
The highest common strength class, for high-load machine assembly. For fine-thread socket head cap screws, 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 |
|---|
Galvanic & Galling Considerations
For fine-thread socket head cap screws 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.
Comparable Grades
For Fine-Thread Socket Head Cap Screws, class 8.8 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of Fine-Thread Socket Head Cap Screws Available in Property Class 12.9 Steel
| Thread series | Drive | Material options | Typical application |
|---|
| metric fine (DIN 912 / ISO 4762) | internal hex | carbon steel / alloy steel / 304 / 316 stainless | precision machinery and moulds |
| UNF (ASME B18.3) | internal hex | carbon steel / alloy steel / 304 / 316 stainless | automotive components |
| UNF (ASME B18.3) | internal hex | alloy steel | general equipment assembly |
Dimensions are independent of the material: every size above is available in Property Class 12.9 Steel.
Custom manufacturing · Made to drawing
Need this screw in a grade that is not listed?
Grade 12 9 Steel is one of the grades the catalog describes. Where the standard stops, the drawing takes over: fine pitches, left-hand threads, partial threading, and property classes above the catalogued grade where material and heat treatment allow. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
Custom screw manufacturingSend a drawing
Applications & Industries
The sectors that buy Fine-Thread Socket Head Cap Screws to DIN 912 / ISO 4762 and ASME B18.3 (UNF), and the duty each one buys them for. Stocked from metric fine (DIN 912 / ISO 4762) to UNF (ASME B18.3) (nominal diameter).
Industries that specify Fine-Thread Socket Head Cap Screws
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Precision machinery
Closer preload control than a coarse thread.
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Automotive components
UNF variants for inch-threaded assemblies.
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Equipment assembly
Stainless options where the joint is exposed.
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Mould and die work
Fine pitch holds setting in a joint that is adjusted often.
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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.
Typical applications
- matching metric fine or UNF to the tapped hole
- choosing 304 or 316 for the exposure
- using a correctly sized hex key to protect the socket
- selecting fine pitch where preload must be set precisely
- 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 force a fine-thread screw into a coarse tapped hole; a few turns of apparent engagement destroys both threads.
- 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 Fine-Thread Socket Head Cap Screws are used, how to specify them, and the cases they are wrong for
