How to identify thread

A wide variety of thread types are used in components like fittings, filters, valves, manifolds, connectors, quick couplings, purifiers, regulators and instrumentation. When choosing the right components for your application it is essential to order the right type of thread and take into account the compatibility of the connection made.

For measuring thread you need:

• a caliper
• a thread gauge
• a table to match your information

We have sent out a small batch of Teesing toolkits to our customers containing a thread gauge for measuring metric and whitworth thread and a small booklet to get you started.

Measuring thread in 4 steps

STEP 1
Determine if the thread is straight (parallel) or tapered. The thread is tapered if the diameter increases or decreases. If the diameter stays the same the thread is straight (parallel).

For example:
Tapered thread (BSPT and NPT).
Straight thread (BSPP and metric).

STEP 2
Measure the thread diameter. Measure the thread diameter using a caliper to determine the diameter and measure on the thread tops.

• For tapered thread: measure on the 4th or 5th full thread.
• For straight thread: measure on any full thread corridor.

STEP 3
Determine the number of threads per inch (TPI) or the pitch (metric threads) with the thread gauge. Use the Teesing thread gauge to determine the pitch or the TPI.The pitch is indicated in metric thread in millimeters. Whitworth thread is indicated in the number of threads per inch.

Locate the possible TPI or pitch by matching the diameter measured with the thread tables below.

STEP 4
Determine the thread standard. Use the parameters obtained in the steps 1, 2 & 3 in order to find the appropriate thread in the table. You have the following information:

• Male of female
• Straight or tapered
• Diameter
• Pitch/TPI

Note: if diameter and pitch do not match those in the table the thread standard is different (it may be NPT).