How to Use a Thread Gauge

There are times it becomes necessary to know the thread pitch of a bolt or nut. A comparison can be made with bolts of known sizes, or a special tool called a thread gauge can be used. This tool looks like a collection of several small saw blades pinned together on one end and each with a different number of teeth. These blades are stamped with a small number which indicates how many teeth per inch the blade has. When fitted against the threads of a bolt or nut the number indicates the bolt thread pitch.

Things You'll Need

• Thread gauge

Instructions

1. Hold the bolt to be measured with the light behind it in the fingers of one hand.

2. 

   Open the thread gauge and place on of the blades against the bolt threads. If the teeth fit tightly against the threads you selected the proper blade on your first try. If not, use other blades until the teeth fit the bolt threads perfectly.

3. Read the number stamped into the blade to determine the threads per inch.

4. Insert the blade inside a nut to measure and count the threads. Fit and read the blade exactly the same as for a bolt.

Tips & Warnings

• Threads may be SAE or metric, buy a thread gauge which has the capacity to measure both types.