Understanding Thread Measurement for Solenoid Valves: A Comprehensive Guide
Measuring a thread size can be tricky, there are several ways depending on the thread type i.e. parallel (straight thread) or taper (conical), BSP (British standard pipe) or NPT (National Pipe Tapered) etc. Then you either have a male thread (external thread) or female thread (external thread). We can go into more detail with regard to the number of threads per inch (TPI), thread depth, thread design etc, but for now we will keep it simple.
So, most UK and EU threads are BSP (G) threads, NPT is more commonly used in the USA and Canada, so by accurately measuring the internal or external common UK BSP thread you should be able to determine what thread you actually have.
1. Recognising Common Thread Types
BSP Threads: Predominantly used in the UK and Europe, BSP threads come in two forms:
BSPP (Parallel): Also known as "G" threads, these have a constant diameter and require a gasket or O-ring for sealing.
BSPT (Tapered): These threads taper along their length and seal by thread interference, often with the aid of PTFE tape or sealant.
NPT Threads: Common in the USA and Canada, NPT threads are tapered and seal through thread interference, typically using PTFE tape or thread sealant.
Key Differences:
Thread Angle: BSP threads have a 55° angle, while NPT threads have a 60° angle.
Sealing Method: BSPP requires a gasket; BSPT and NPT seal via thread interference.
2. Measuring Thread Sizes
Step 1: Determine Thread Type
Male (External): Measure the outside diameter (OD) of the thread.
Female (Internal): Measure the inside diameter (ID) of the thread.
Step 2: Measure Diameter
Use a calliper to measure the OD or ID accurately.
Note: The measured diameter may not correspond directly to the nominal pipe size. For example, a male thread measuring approximately 26.4mm (just over 1 inch) is actually a 3/4" BSP thread.
Step 3: Identify Threads Per Inch (TPI)
Use a thread pitch gauge to count the number of threads per inch.
Compare your measurements to standard thread charts to identify the thread size and type.
3. Standard BSP Thread Dimensions
| Nominal Size | Threads per Inch (TPI) | Major Diameter (mm) |
|---|---|---|
| 1/8" | 28 | 9.728 |
| 1/4" | 19 | 13.157 |
| 3/8" | 19 | 16.662 |
| 1/2" | 14 | 20.955 |
| 3/4" | 14 | 26.441 |
| 1" | 11 | 33.249 |
| 1 1/4" | 11 | 41.910 |
| 1 1/2" | 11 | 47.803 |
| 2" | 11 | 59.614 |
| 2 1/2" | 11 | 75.184 |
| 3" | 11 | 87.884 |
Note: Always refer to standardized charts for precise measurements, as nominal sizes may not match actual measurements directly.
4. Tips for Accurate Thread Identification
Avoid Assumptions: Do not assume thread size based solely on measured diameter. Always cross-reference with standard charts.
Use Proper Tools: Employ callipers and thread pitch gauges for accurate measurements.
Consult Standards: Refer to relevant standards (e.g., ISO 228 for BSPP, ISO 7 for BSPT) for detailed specifications.
5. Additional Resources
Valve Search Wizard: Utilize our Valve Search Wizard to find valves based on thread size and type.
Contact Us: For further assistance, reach out to our technical team at sales@solenoid-valves.com or call 01454 334 990.
Helpful hint: Don't assume if you measure a thread as 25.4mm that it is 1" BSP, it does not work that way, see table below for guidance.
A male thread that measures 26.4mm (just over 1 inch) is actually 3/4BSP.
See below dimensional thread guide for BSP threads.
Use our valve search Wizard to help you. See port size and click the question mark to view dimensions
Try our search wizard.
