Square Nut are used primarily for the clamped counter-face of a bolted joint. This page lists the industries and assemblies where they are specified, the selection criteria that matter for each application, installation practice, and the cases where a different fastener type is the correct choice. Parts are supplied to GB/T 39 / ISO 4034. Stocked across roughly M3 to M24, they cover general to heavy-duty work.
Typical Applications for Square Nut — GB/T 39 / ISO 4034 (Series 075)
The most common settings where these are specified:
- Vibration-prone equipment: where a locking or flanged style resists loosening.
- Frames & weldments: captive or welded options for repeatable assembly.
- General machine building: fastening covers, brackets, motors and sub-assemblies on production equipment.
- Maintenance & repair (MRO): a stocked size for servicing existing plant where the original fastener spec must be matched.
- Fabrication & metalwork: bench and on-site assembly of steel frames, enclosures and weldments.
How to Specify Square Nut — GB/T 39 / ISO 4034 (Series 075) for Your Application
- Size: Match the nominal size to the mating thread or hole. This product spans M3–M24; check the full table below for the exact dimensions of each size.
- Locking & grade: Match the strength grade to the bolt, and choose a locking style (nyloc, all-metal, serrated flange) if the joint sees vibration.
- Environment: For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient.
- Standard: This product is supplied to GB/T 39 / ISO 4034. Quoting the standard on your order guarantees interchangeable dimensions between suppliers.
Installation & Assembly Practice
- Run the nut down by hand before applying the wrench to catch cross-threading early.
- Tighten the nut rather than the bolt head where access allows — the torque-to-preload relation is more consistent.
- For locking styles, note that nyloc inserts are single-use in critical joints and lose grip above roughly 120 °C.
Common Selection Mistakes with Square Nut — GB/T 39 / ISO 4034 (Series 075)
- Pairing a high-class bolt with a lower-class nut — the nut strips before the bolt reaches proof load; the nut class must meet or exceed the bolt class.
- Using a plain nut with a spring washer in severe vibration instead of a prevailing-torque locking nut.
- Re-using nyloc nuts in critical joints.
Where Square Nut — GB/T 39 / ISO 4034 (Series 075) Are Not the Right Choice
Not on their own — they need a matching bolt or stud — and a plain nut is not a substitute for a locking type under heavy vibration.