Thread gages are used to measure a thread's pitch diameter and functional size. This is done by calibrating the tool to a master thread that has been accurately measured.

But what are the main types of British thread gages? How do they differ? Read on to learn more.

Unilateral Thread Gages

As the name suggests, unilateral thread gages only measure one side of the thread. They are used to check for major diameter, pitch diameter, and functional size. The major diameter refers to the largest width of the thread, while the pitch diameter is in-between the crests and roots.

Unilateral gages can be used on both internal and external threads. This makes them very versatile, as they can be used on various parts. They are also quite affordable, which makes them a popular choice for many businesses.

Concentric Thread Gages

Concentric thread gages are used to measure the pitch diameter of a thread. Unlike unilateral gages, they can only be used on internal threads. This is because they have a three-point contact design, which means that they can only fit inside a hole. As such, they are only used to measure the pitch diameter, not the major or functional size.

While they may be more limited in terms of application, concentric thread gages are more accurate than their unilateral counterpart. This is because they evenly distribute the pressure along the entire length of the gauge, which leads to more accurate measurements. They can also measure threads of all sizes due to their wide variety of size options.

Plug Thread Gages

Plug thread gages are used to measure a thread's major diameter, pitch diameter, and functional size. They can be used on both internal and external threads, which makes them just as versatile as unilateral gages.

These gages rely on parallel-sided cones instead of points to make contact with the thread. This design helps to distribute the pressure evenly, giving them a tighter tolerance. This, in turn, leads to more accurate measurements. It also helps prevent the gage from getting stuck in the thread. In addition, their design also makes them more durable, as there is less chance of them breaking under pressure.

While they may be more accurate and durable, plug thread gages are also more expensive than other types of gages. This is because they are often made from higher-quality materials and require more precision to manufacture.

British thread gages come in many different shapes and sizes. While they all serve the same purpose, they each have their own unique features that make them better suited for certain applications. It is important to choose the right gage for the job to get accurate measurements.