During the past few years, I’ve found myself encountering more customers requiring gauge repeatability and reproducibility (GR&R) studies performed on thread gauges. When I say, “thread gauges,” I’m really referring to indicating thread gauges; you might refer to them as “snap gauges” or “tri-rolls.”

When preparing to run a GR&R study with an indicating thread gauge, there are several factors to be aware of prior to setting up. First is the actual form of the thread. Unlike a plain diameter part, a screw thread has several unique characteristics that make running a GR&R more complicated. All screw threads have three diameters: major, pitch, and minor. They also have helix, flank angles, and pitch, which is commonly associated with the lead of the thread. (Lead is defined as one axial advance per unit rotation.) How far does the part move when you rotate it 360°? If a part has a pitch of 1.0 mm, it should advance 1.0 mm.

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