If you are rather new to the idea of the metrics of fasteners and how they made, sifting through things like thread gages and thread plug gages can be a little confusing for sure. There are so many different terms used to describe the tools that are used to take measurements and metrics of threaded screws, bolts, or other fasteners that finding what you really need can be tough. To be an educated shopper and get what it is you are going for, it is important that you do understand some of the most basic terms. Here is a look at some of the terms commonly used in reference to thread gages.
Pitch Diameter
Pitch diameter is a measurement that is taken between one point on the thread of a screw to another point. For most purposes and metric terms, the pitch diameter will be measured from about the central part of a thread to the same point of reference on the neighboring thread. Pitch gages are designed to take these measurements; the distance between one thread and the next.
Major and Minor Diameter
Major diameter and minor diameter are two typical terms used in thread gaging. Major diameter refers to the diameter of a screw or bolt, or, in other words, the threaded exterior of an elongated piece. Minor diameter is referring to interior diameter, such as the interior of a threaded nut. Knowing major and minor diameter is important when picking thread gages, especially plug-style gages because the diameter will determine if the gage will fit the piece properly.
Flank Angle
In the most general terms, a flank angle is the measurement of the angle between the flank of the screw and its angle from the main axis of the screw. For example, some screws have steep flank angles with a narrow angle between the flared cut and the screw's primary central axis point and some screws will have a wide-set flank angle in which the threads set out closer to a 90-degree angle. When measuring threads, the flank angle can be an important factor to take note of because this angle also has an effect on the overall distance between threads.
With a little terminology understanding, you will have no trouble picking out thread gaging tools to handle whatever task it is you have to deal with. Talk to an industrial equipment supplier for more information about thread gages..
