How to Measure NAS Bolts

Set the dial calipers to zero. Close the jaws on the calipers. Loosen the adjustment screw on the dial face. Rotate the dial so it reads exactly zero.

Measure the overall length of the NAS bolt from under the bolt head to the end of the threads. This is the overall under head length.

Lay the open jaws of the caliper against the threads. Measure the length of the threads. This is the NAS bolt thread length.

Subtract the overall head length from the thread length. The final calculation is the grip.

Confirm the grip by measuring it with the calipers. When finding the total grip length be sure to add the thickness of washers used under the bolt head.