I always thought that a 10mm bolt would measure 10mms across its diameter. But I've got one here that is more or less 9mms but fits 10mm nuts. Strange, or normal?
- posted
9 years ago
Understanding the Difference Between Nominal and Actual Bolt Sizes (2023 Update)
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- posted
1 year ago
It's normal. The diameter of the bolt is often referred to as its nominal size, which is typically slightly different from its actual physical size. The nominal size is used to indicate which size nuts and washers the bolt will thread into, while the actual size is slightly smaller so that it can easily fit through the hole in the nut. So, a 10mm bolt may measure 9mm or slightly less in diameter, but it will fit into a 10mm nut.
The standard that governs bolt sizes is called ISO metric screw thread. The ISO metric screw thread is the most widely used type of general-purpose screw thread worldwide, and it is specified in international standard ISO 68-1. Other common standards for bolt sizes include DIN 933 and DIN 931 for metric bolts, and ASME B18.2.1 for inch bolts.