UNR, UNJ, M, and MJ Threads

UNR bolts are to be used with UN nuts. No UNR nut specification exists. UNR bolts are very similar to UN, but the sharpness of the curvature in the bolt thread root is specifically limited to reduce stress concentration. This is particularly beneficial in fasteners subjected to cyclical loading which causes fatigue. We could add a UNR calculator to these pages without much difficulty, but we will not do it unless people clamor for it. And even then, we might only include a UNR calculator in the Windows version of the calculator.

UNJ bolts are like UNR, but the curve of the bolt thread root is even more gentle which requires the thread root to be shallower. In fact, the thread root is so shallow that the bolt thread cannot mate with a UN nut, so there is a UNJ nut specification as well. As with UNR, we could add a UNJ calculator to these pages without much difficulty, but we will not do it unless people clamor for it. And even then, we might only include a UNJ calculator in the Windows version of the calculator.

M and MJ are similar to UN and UNJ, respectively, except that they are measured in metric units and the sizes are metric sizes. The smallest UN size is #0, but there are smaller sizes that are standard in the M series, so the small M sizes are recommended when a size smaller than UN #0 is required. As with UNR and UNJ, we could add M and MJ calculators to these pages without much difficulty, but we will not do it unless people clamor for it. And even then, we might only include these in the Windows versions of our calculators.

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