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Five Basics Of Measuring A Hydraulic Fitting

Ensuring the correct size of fitting to match your hose is essential, in our latest blog, we’re giving you the five basics of measuring a hydraulic fitting.


Before you select a hydraulic fitting, you must first determine if its threads will match the hose you have selected. Measuring and identifying the fittings is easily done but you must have the correct tools. These tools include ID/OD calipers and thread pitch gauges.


A diligent approach to measuring a hydraulic fitting can help you avoid leaks and downtime. Even to a professional, two hydraulic fittings can look identical while being completely different. An incorrectly sized fitting may seem to fit at first, but with time it can cause problems throughout your system.


Mismatched fittings are one of the most common problems with hydraulic systems, but are also the easiest to avoid.


Tools Needed:

  • Measuring tape
  • Callipers
  • Thread pitch gauge
  • Protractor


1) Measure The Length

Using the thread pitch gauge, simply place the gauge teeth on the threads until a tight fit is found. Ensure that there is no gap between the teeth of the gauge and the fitting. If the fitting is not new or worn, you may have difficulty finding a match so it’s best to always use new fittings. Fitting manufacturers provide thread identification guides either in brochures or on their websites, so you simply need to match the thread measurement to the relevant charts.


2) Determine The Outside Diameter

The outside diameter (or male thread) of a fitting is determined with the assistance of callipers. Zero out the callipers, put the fitting between the jaws and close them to hold the fitting tight.

A Vernier calliper provides highly correct readings. You may want to measure the diameter several times to make sure you are getting the right results.


3) Calculate The Inside Diameter

The inner diameter (or female thread) is also measured with callipers. The process is similar. However, this time, you have to place the calliper jaws inside the fitting in order to get the precise readings.


4) Evaluate The Thread Gauge

The thread pitch gauge determines the distance between threads. Put the gauge on the threads to get a snug fit. You can then match the measurements to a size chart. In case you don’t have a thread pitch gauge, you can roughly determine the thread gauge using Vernier callipers. Count the number of threads within a one-inch distance.

For British and European threads, the thread gauge is measured in threads per inch. Metric threads of a gauge determine the distance between the threads.


5) Estimate The Angle

Use a protractor to determine the angle of the fitting. The angle is one of the most important factors when choosing the right new fitting for your hydraulic system. The most common angles are 45° and 90°. However, you can occasionally face 22.5° angles on elbow fittings.


Things To Consider

When measuring the old fitting, it’s important to remember that wear and tear may have changed the measurements slightly. It’s important to get a professional opinion about fitting sizing in case the measurements of your old fitting don’t match the charts.


Understanding some of the most common connector types will help in identifying and measuring them in thread identification guides. NPTF (National Pipe Tapered Fuel) connectors are used in fluid power applications although not recommended. Other common designs are NPT, SAE J514 JIC/37°, SAE J1926 straight thread O-ring boss, SAE J512 45°, SAE J1453 O-ring face seal, ISO and DIN connectors, among others.




For more information on measuring fittings or for help and advice, get in touch with our technical team, we’re here to help.

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