The measuring of threads on a hydraulic fitting requires a certain technique that needs to be carefully followed. This procedure requires the correct tools, specifically ID/OD calipers and thread pitch gauges, which will be used to measure and identify the threads.

It is first necessary to determine whether the threads of the fitting match the hose being used. This can be accomplished by placing the teeth of the pitch gauge on the threads to the point that they fit tightly. It is also important to ensure that no gap exists between the fitting and the teeth gauge. This method is illustrated in Figure 1. Through information provided in their brochures or on their websites, manufacturers can make this process easier by allowing you to simply match the thread measurement with the corresponding data chart. However, components that are worn may not match properly despite your use of the proper technique, which is why it is always wise to use new fittings.

Two measurements will be needed to complete the procedure. Measuring the outer diameter, or the male thread, will require placement of the ID/OD caliper snugly around the fitting. The inner diameter, or the female thread, is measured by inserting the caliper into the fitting and then matching this information with the manufacturer’s data. This method is illustrated in Figure 2. In order to be done properly, you will have to determine whether the fitting is tapered, or machined in an angled manner, or parallel, with the threads running at the same width throughout the piece.

Identification of the most common connectors will help in the measuring process. The most common types include the SAE

J514 JIC/37-degree, SAE J1926 straight thread O-ring boss, SAE J512 45-degree and SAE J1453 O-ring face seal, and DIN, ISO and NPT connectors. National Pipe Tapered Fuel (NPTF) connectors, which are used in fluid power applications, are otherwise not recommended.