bgbailey@parker.com

Construction equipment, like virtually everything else, is a global industry with design and manufacturing coming from every corner of the world. The hydraulic systems alone use countless different types of fittings and adapters, with differences in sealing methods and differences in the thread forms. Nearly every country has a different standard-which can make it difficult to accurately identify the threads on fittings and adapters when equipment modifications or repairs are needed.

Usually, the style of fitting or sealing principle is easy to distinguish by appearance but the thread forms all seem to look the same. There are six common types of threads that are used on hydraulic tube fittings. We will learn how to identify all six.

Most people are aware of "American pipe threads" (NPT/NPTF) and also, what is often called "SAE threads" or "Unified threads" (UN/UNF). But, there are other unfamiliar threads that are usually classified as "metric threads" regardless of whether they are really metric. In reality, there are threads that are truly metric and there are also BSP (British Standard Pipe) threads.

The six different thread types are: 1) UN/UNF, 2) NPT/NPTF, 3) BSPP (BSP, Parallel), 4) BSPT (BSP, Tapered), 5) Metric Parallel, and 6) Metric Tapered. Three of these are parallel (UN/UNF, BSPP, Metric Parallel) and three are tapered (NPT/NPTF, BSPT, and Metric Tapered). Three are pipe threads (NPT/NPTF, BSPT, and BSPP) and three are not (UN/UNF, Metric Parallel, and Metric Tapered). Keep in mind that tapered does not necessarily mean that it is pipe thread (e.g., metric tapered) -and the fact that it is pipe thread, does not mean that it cannot be parallel (e.g., BSPP).