How to Identify Thread Pitch and Size
Thread pitch is a critical measurement used to identify and differentiate threaded connections in fluid systems. Because many thread types can appear similar, accurately determining thread pitch is an important step in selecting compatible components and helping prevent leaks, rework, and connection failures. In this video, you'll learn what thread pitch is, how it is measured, and why it plays a key role in thread identification and system assembly. Understanding thread characteristics, along with other factors such as thread form and sealing method, can help improve component selection and maintenance practices.
Video Transcript
Welcome to this Swagelok how‑to video. In this segment, we’ll look at identifying thread pitch and size. Thread pitch concerns are very important to anyone who uses fittings or any threaded components.
Here’s what you’ll need for the procedure shown in this brief video: a caliper, a pitch gauge, and a thread pitch identification guide. Let’s take a look.
Threads have peaks and valleys, referred to as crests and roots. The surface between the crest and the root is called the flank.
Tapered threads—sometimes called dynamic threads—are designed to seal as the flanks of the mating threads are drawn together. Thread sealant is required to fill the gaps between the crests and roots to prevent system fluids from penetrating the connection.
Straight threads—also called parallel threads—are not designed to seal. They rely on other factors such as a gasket, an O‑ring, or metal‑to‑metal contact to create a leak‑tight seal.
The first step in identifying thread size and pitch is determining whether the thread is tapered or parallel. Tapered threads are at an angle relative to the centerline, while parallel threads run parallel to the centerline.
Using a caliper, measure the nominal male or female thread crest‑to‑crest diameter on the first and last full threads. If the diameter increases on a male end or decreases on a female end, the thread is tapered. If all diameters are the same, the thread is straight.
Next, use the caliper to measure the nominal thread diameter from crest to crest. For tapered threads, measure the fourth or fifth full thread. For parallel threads, measure any full thread.
The next step is determining the thread pitch. Use a pitch gauge and check the thread against each form until you find a match. Some fractional and metric thread forms are very similar, so this may take a little time.
The final step is determining the thread standard. Take the information you’ve gathered—thread category, nominal diameter, and thread pitch—and use a thread identification guide, such as the Swagelok Thread and Connection Identification Guide, to identify the thread.
Refer to swagelok.com for additional information. Thank you for watching. We will continue developing videos like this to help you get the job done. Get more information by watching our other videos or contacting your authorized sales and service center.
