Understanding nut dimensions is crucial for ensuring compatibility with screws and bolts. Measuring nuts is generally easier than measuring screws, and this guide will walk you through the basics.
Measuring Nut Size
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Nut size is typically defined by the inner diameter, which determines the screw it fits.
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For example, a 5/16" nut or 8mm nut fits any screw with the same major nominal diameter.
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Home improvement stores, like Home Depot, often use only the inner diameter for sizing nuts.
How to Measure:
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Use the side parts of a screw gauge to measure the nut.
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Place the hole of the nut around the gauge until it fits snugly.
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Alternatively, if uncertain, check which screw the nut fits and use that screw’s major nominal diameter as the nut size.
Measuring Thread Pitch
Some nuts are also specified by thread pitch, which refers to the number of threads per inch (TPI).
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For example, a nut labeled 1/2in.-10 has 10 threads per inch.
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To measure pitch manually:
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Use calipers to measure the depth of the threads in the nut (e.g., 5mm ≈ 0.2in).
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Count the number of threads within that depth (e.g., 3 threads).
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Divide the thread count by the depth in inches:
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This nut could then be classified as a 5/16in.-15 lock nut.
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While there are more advanced tools for precise measurements, this method works well for most practical purposes. The inner diameter remains the most important measurement for selecting a compatible nut.