Industrial and machinery fasteners — bolting you can quantify
Production machinery fails at joints before it fails at components. This page covers how to specify property class, thread form and coating so that a bolted joint performs as designed rather than as assembled.
Selecting property class for a machinery joint
| Class | Tensile strength | Typical use | Important limitation |
|---|---|---|---|
| 4.8 | 400 N/mm² | Non-critical brackets, covers, light assemblies | Low preload — not suitable for dynamic loading |
| 8.8 | 800 N/mm² | General machinery, structural steelwork, most bolted joints | The default choice unless there is a reason to go higher |
| 10.9 | 1,040 N/mm² | High-preload joints, engine and transmission bolting, wind and tower structures | Hydrogen embrittlement risk with electroplated coatings — specify de-embrittlement baking |
| 12.9 | 1,220 N/mm² | Socket head cap screws in moulds, dies, robotics, high-stress fixtures | Most sensitive to embrittlement; prefer black oxide or zinc-flake coatings over electroplating |
| A2-70 / A4-80 | 700 / 800 N/mm² | Corrosive environments, food and chemical plant, marine | Galling risk on stainless-to-stainless threads — specify a lubricant or a dissimilar pair |
Where industrial buyers most often get caught out
Coating vs. embrittlement
Electroplated class 10.9 and 12.9 parts can absorb hydrogen during pickling and plating. If the coating is not followed by a de-embrittlement bake, delayed fracture can occur weeks after assembly. Specify it explicitly.
Thread form mismatch
Metric coarse, metric fine and inch threads are not interchangeable, and DIN vs ASME head dimensions differ in ways that matter for socket access. Buy to the drawing, not to "M12 bolt".
Mixed batches
Two coating types with the same part number is a real failure mode in mixed containers. We pack and label by coating so the assembly line cannot pick the wrong part.
Galling on stainless
A2 and A4 threads under high torque can seize and shear. Use a lubricated or nitronic pairing, or slow the assembly speed on powered tools.
Hardware used in this application
High Tensile Bolt 10.9 / 12.9
10.9 high tensile bolt manufacturer
Socket Head Cap Screw DIN 912
DIN 912 socket head cap screw supplier
Stud Bolt DIN 976
DIN 976 stud bolt supplier
Nylon Insert Lock Nut DIN 985
DIN 985 nylon lock nut supplier
Flange Nut DIN 6923
DIN 6923 flange nut supplier
Threaded Rod DIN 975
DIN 975 threaded rod supplier
Rivet Nut (Blind Nut)
rivet nut manufacturer China
Weld Nut (Projection Welding)
weld nut manufacturer China
Frequently asked questions
Can you supply first-article inspection reports?
Yes. For production runs we issue a first-article inspection report covering the full drawing before the batch is released, which is usually a condition of OEM supplier approval.
Do you work to customer drawings with locked specifications?
Yes. Once a specification is agreed it is locked, with change control: if the producing factory, material source or coating process changes, you are informed before the change takes effect.
How do you control heat treatment?
Partner factories heat treat to ISO 898-1 with calibrated furnaces and record hardness and, where required, tensile, proof load and impact results per heat number.
Can you reduce the number of part numbers we carry?
Often yes. Reviewing the bolt schedule frequently reveals that several similar sizes and classes can be consolidated onto one standard, which reduces inventory and the risk of the wrong part being fitted.
Ready to source quality hardware from China?
Tell us the application, the environment and the volumes — we will propose a specification rather than just quoting a part number.