Six Most Common Types of Threads:

  1. UN/UNF
  2. NPT/NPTF
  3. BSPP (BSP, parallel)
  4. BSPT (BSP, tapered)
  5. metric parallel
  6. metric tapered

How to identify different types of threads in four easy steps

Before you start, make sure you have two thread identifying tools on hand:

Pitch Gauge

A pitch gauge is a tool used to measure the distance between the crests of threads. For NPT, UN/UNF, BSPP, and BSPP we measure the number of threads per inch. If you have the metric threads, the pitch gauge identifies the distance between each individual crest in millimeters.

Caliper

A caliper is used to measure the diameter of a thread. For male threads, it measures the outside diameter, for a female thread – inside diameter, respectively. For advanced users, a digital caliper is available from multiple retailers. It saves your time and simplifies the process.

STEP 1. Parallel thread vs. tapered thread. Let’s learn the difference.

Parallel threads include:

UN/UNF

BSPP

metric parallel

Tapered threads include:

NPT/NPTF

BSPT

metric tapered

To identify whether the thread is tapered or parallel, look at the diameter of your thread. If the thread diameter gets thinner towards the end, you are looking at a tapered thread. On the contrary, if the thread diameter is the same at the top and the bottom of the thread, you have the parallel thread. See the graphics below to learn the visual difference between tapered and parallel threads.  Using a known parallel, like a pair of calipers can help to show if a fitting is tapered.  If the threads touch the entire length of the calipers, it is parallel but if it rocks you have tapered threads.

STEP 2. Determine the Pitch

Use a thread pitch gauge tool to determine the size of the thread. Thread pitch gauge helps you to accurately measure and calculate the number of threads within a given distance.

STEP 3. Thread size matters

When it comes to determining the thread size, you have two approaches at your disposal. Before you start, determine if your thread is a pipe thread (NPT/NPTF, BSPT, BSPP) or not (UN/UNF, Metric Parallel, Metric Tapered). Remember that tapered thread can both be a pipe thread or not.

If you have a pipe thread, compare the size of the thread with a nominal size profile, For non-pipe thread (UN/UNF, Metric Parallel, Metric Tapered), use the caliper tool to measure the outside diameter of the tread.

STEP 4. Designate the thread

This step involves designating the thread according to the industry standards for further use. Start with identifying the tread size (nominal or actual), then write down the type and the pitch (if applies).

QC Hydraulics can manufacturing UNC/UNF, NPT/NPTF, BSPP, BSPT, Metric parallel and metric tapered thread. If you have any demand of them, please feel free to contact me.

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