| Standard | Title | Application |
| ISO 898-2 | Mechanical properties of fasteners made of carbon steel and alloy steel – Part 2: Nuts with specified proof load values | Provides general mechanical testing requirements; widening may be evaluated as a deformation criterion |
| ISO 2320 | Prevailing torque type steel nuts – Mechanical and performance requirements | May involve nut dilation during functional testing of locknuts |
| (Internal OEM or industry-specific standards) | Custom procedures or manufacturer specifications | Often used when no explicit international standard defines the method |
| Standard | Title | Notes |
| ASTM F606 / F606M | Standard Test Methods for Mechanical Testing of Fasteners | Allows measurement of deformation, though “widening” is not explicitly named |
| (OEM Standards) | Manufacturer-specific test protocols | May define radial growth limits for critical applications (e.g. aerospace, energy) |
| Parameter | Description |
| Axial proof load | A calibrated axial load is applied through a mandrel or test stud |
| Measurement before/after | Internal diameter across corners or flats is measured before and after loading |
| Deformation check | Radial growth (ΔD) is checked against allowed tolerance (e.g., ≤ 0.05 mm) |
| Failure mode | Failure is defined by exceeding dimensional growth or visible cracking |
| Typical setup | Press or tensile machine with nut mounted on hardened mandrel |
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