Baker manufactures hole location plugs as shown. These are used to measure & check the location of small tapped holes. This is a perfect gauge to inspect features for run-out to the pitch diameter of the threads. These give a firm locating grip without pulling the shoulder of the plug up against the hole face thus avoiding squareness errors.
Hole location plugs are commonly used to measure the location of tapped holes. It is difficult to accurately measure the location of tapped holes using conventional methods; i.e. CMM’s or indicating type instruments. Hole location plugs are deliberately manufactured with Pitch diameter over-size, then slitted, resulting in the threaded section collapsing while being screwed in the threaded hole. The hole location plug will screw in tightly, locating on the Pitch diameter of the tapped hole. A measurement can then be taken from the datum point to the cylindrical diameter on the hole location plug to determine location. For very small sizes, the plug is not slitted but the thread is manufactured with a gradual taper, which will lock up on the thread.