Many standards exist relating to fasteners that detail geometry, mechanical properties, and finishes. At times, differentiating between these variations can be difficult. Below are a few of the most common standards for both inch fasteners and metric fasteners:
Inch Fasteners
| Fastener | Dimensions | Mechanical & Material Properties |
| Hex head cap screws | ANSI/ASME B18.2.1 | SAE J429 |
| Hex nuts | ANSI/ASME B18.2.2 | SAE J995 |
| Hardened steel washers | ASTM F436 | ASTM F436 |
| Unhardened steel washers | ASTM F844 | ASTM F844 |
Metric Fasteners
| Fastener | Dimensions | Mechanical & Material Properties |
| Hex head cap screws | ISO 4014/ISO 4017 | ISO 898-1 |
| Hex nuts | ISO 4032 | ISO 898-2 |
| Hardened steel washers | ISO 7089 | ISO 7089 |
| Unhardened steel washers | ISO 7091 | ISO 7091 |
Most inch fastener standards have only one standard which governs dimensional characteristics of a part, but metric fasteners may have many standards. These standards are often the same, with a few notable exceptions:
Variations
| Fastener | Preferred Standard | Standard option 2 | Standard option 3 | Difference |
| Hex head cap screws | ISO 4014 | ANSI/ASME B18.2.3.1M | DIN 931 | Width Across Flats (WAF) is larger on select sizes for DIN fasteners |
| Hex nuts | ISO 4032 | ASME B18.2.2M | DIN 934 | The thickness of DIN nuts is slightly lower |
For metric fasteners, we recommend using ISO standards as they are the most recognized and used all over the world. Some catalogs still list DIN standard parts even though the DIN standard may be obsolete, and parts are still made to these obsolete standards. If you have any questions on which standard part is right for your build, contact us at ProvenProductivity@bossard.com for more information.
Everything You Need to Know About Inch and Metric Fastener Standards by Bossard
