The hydraulic systems of Industrial machines and equipment use different types of countless fittings and adapters with different sealing methods and thread forms, furthermore the sealing methods can often be distinguished by appearance, thread forms all seem to look the same, making it difficult and time-consuming to identify them when equipment modifications or repairs are needed.
Identifying the correct thread is critical in selecting the right replacement parts for maintenance and repair in order to avoid damage to the thread during installation, which compromises the pressure holding capacity and seal reliability of the fitting or adapter. Swift and proper identification of threads can help maintain safe, productive and profitable operations. There are six types of threads commonly used on hydraulic tube fittings:
To determine if the thread is tapered or parallel: NPT/NPTF and BSPT are tapered threads while UN/UNF and BSPP are parallel. Tapered threads get smaller in diameter toward the end of the fitting while parallel threads maintain the same diameter from start to finish. If there are any deviations by looking at the fitting, use the parallel jaws of a caliper to make a comparison.
To determine the pitch: This can be deciphered using a pitch gauge for comparison or to accurately measure and calculate the number of threads within a given distance. It is much easier to compare threads against a lighted background with a pitch gauge and it is advisable to try a number of gauges before deciding which one fits best.
To determine the size: Combining the results of Steps 1 and 2 will determine – or help predict, in some cases, the correct procedure for Step 3. There are two methods for determining the thread size depending on whether the thread is a pipe thread (NPT/NPTF, BSPT, BSPP) or is not a pipe thread. Keep in mind that tapered (as determined in Step 1) does not necessarily mean that it is a pipe thread (e.g., Metric Tapered). Likewise, pipe thread can be parallel (e.g., BSPP).
To designate the thread: This final technical step does not pertain to identifying the thread. Rather, it is a method of designating the thread type in an industry-standard format for others to understand.
These 4 step processes can help your company’s maintenance and repair professionals and minimize machine downtime, avoid the expense of acquiring (and returning) incorrect parts and help ensure a safe, accident-free work environment.