Metric hex nut specs

Written by john walker
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Metric hex nut specs
Nut specifications detail what type of bolts the nut matches. (bolt image by Sergey Galushko from

Nuts and bolts are used in countless applications. Metric hex nuts are some of the more common nuts. A metric hex nut is hexagonal-shaped and uses the metric system to measure the size of the nut, size of the internal threads, and the distance between threads. The measurements equate to the exact specifications of each type of metric hex nut.

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A metric nut fits metric bolts and screws only. The size outline is classified in an "M" code, such as M10x1.50. M10 implies that the nuts fits a 10mm wrench. The "M" code does not have to correspond to the size of the bolt. An M6 nut can easily fit on an M10 bolt. Most applications use nuts of the same size as the bolt for uniformity of appearance and application. The most common sized nuts are M8, M10 and M12, which are found in most household and vehicle applications.


The threads are outlined by the second part of the "M" code. The M10x1.50 indicates that the nut has a distance between each thread of 1.50mm. An M10x1.50 can only fit on a bolt that has a similar thread distance. M12x1.50x30 will accommodate the M10x1.50 nut. The 30 in the bolt measurement is the overall length of the bolt. A M10x1.50 nut will cross-thread a M10x1.25x20 bolt. Cross-threading happens when the threads of the nut and bolt are uneven and end up crossing over each other. Cross-threading will destroy both the bolt and nut.

SAE versus Metric

SAE (Society of Automotive Engineers) uses a similar measurement system for nuts and bolts. The code follows the same layout of the metric nuts and bolts, but it uses Standard or American measurements. An M13x1.50 nut will be similar to a 1/2x13 nut. The two are not interchangeable but have threads that are close in size. Bolts are stamped on the head with SAE or metric measurements. Nuts are not. SAE nuts close in size to a metric equivalent will seem to fit a metric bolt initially but will cross-thread the bolt. Always store your metric and SAE nuts separately.

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