How to Measure Pipe Fittings
Quick Guide: How to Measure Pipe Fittings
- Pipe Size: Measure the inside diameter (ID) for pipes, outside diameter (OD) for tubing.
- Thread Size: Use calipers (or a ruler) to measure the OD of male threads, ID of female threads.
- Thread Pitch: Count threads per inch (TPI) with a thread gauge or ruler.
- Tapered vs. Parallel Threads: If the diameter decreases, it's tapered (NPT, BSPT); if consistent, it's parallel (BSPP, Metric).
- Seat Angle (JIC, SAE): Use a seat gauge or protractor to check flare angles (e.g., 37° JIC).
Why Accurate Measurement Matters
In hydraulic and fluid systems, incorrect pipe fitting measurements can lead to leaks, inefficiencies, and costly downtime. Whether you’re working with NPT, BSP, or JIC fittings, knowing how to measure correctly ensures compatibility and system integrity.
Key Tools Needed for Pipe Fitting Measurement
- Calipers: Essential for measuring outside diameter (OD) and inside diameter (ID).
- Thread Pitch Gauge: Determines the number of threads per inch (TPI) or millimeters.
- Pipe Tape Measure: Helps measure pipe circumference to find diameter.
- Seat Angle Gauge: Required for identifying flare angles (e.g., JIC 37°, SAE 45°).
- Ruler or Measuring Tape: Alternative if calipers are unavailable.
- String & Ruler Method: Useful for estimating pipe circumference.
Step-by-Step Guide to Measuring Pipe Fittings
1. Measure the Pipe Diameter
For Pipes: Measure the inside diameter (ID) – this corresponds to the nominal pipe size (NPS).
For Tubing: Measure the outside diameter (OD) – tubing size is based on the external measurement.
For Hose Fittings: Measure the hose ID to match the correct fitting size.
If No Calipers: Wrap a string around the pipe, mark the overlap point, measure the string length, and divide by π (3.1416) to estimate OD.
* Example: A 1” NPT pipe fitting has an OD of ~1.315 inches but is still called a 1” fitting.
2. Measure the Thread Size
Use Calipers to Measure the Thread’s OD or ID (if available):
- For Male Threads: Measure the outside diameter (OD) across the widest points of the threads.
- For Female Threads: Measure the inside diameter (ID) from crest to crest inside the fitting.
If No Calipers: Use a ruler to measure across the thread’s widest point and compare to standard thread charts.
Use a Thread Pitch Gauge: Match the thread count per inch (TPI) or mm to standard charts.
If No Thread Pitch Gauge: Place a ruler along the thread and count the number of threads within a known distance (e.g., 1 inch or 25mm for metric threads).
* Example: A ¾” NPT fitting has a thread OD of ~1.050 inches.
3. Determine the Thread Type
Check if the thread is tapered or parallel:
- Tapered Threads (NPT, BSPT): Diameter decreases at the end.
- Parallel Threads (BSPP, Metric): Diameter remains consistent.
Compare your measurements to a standard fitting size chart to confirm the type.
4. Identify the Seat Angle (If Applicable)
For Flare Fittings (JIC 37° or SAE 45°):
- Place the fitting against a seat angle gauge to match the angle.
- Look for O-rings in ORFS (O-Ring Face Seal) fittings.
- Flat faces indicate ORFS or BSPP O-ring fittings.
If No Seat Gauge: Use a protractor or compare against a known fitting.
5. Measure Overall Length & Center-to-End Distance
For Elbows and Tees:
- Measure the Center-to-End Distance for proper fitment.
For Straight Fittings:
- Measure end-to-end or overall length.
Common Pipe Fitting Standards
| Standard | Type | Key Features |
|---|---|---|
| NPT (National Pipe Tapered) | Tapered | Thread seals via interference |
| BSPT (British Standard Pipe Tapered) | Tapered | Similar to NPT but different pitch |
| BSPP (British Standard Pipe Parallel) | Parallel | Requires a sealing washer or O-ring |
| JIC (Joint Industry Council – 37° Flare) | Flared | Metal-to-metal sealing |
| SAE 45° Flare | Flared | Used in low-pressure applications |
| ORFS (O-Ring Face Seal) | Flat Face | Seals via O-ring, high-pressure tolerant |
| Metric Fittings (DIN, ISO, BSP, JIS) | Varies | Metric thread standards |
Frequently Asked Questions
How do I know if my fitting is BSP or NPT?
- Measure the thread pitch (BSP uses metric, NPT uses TPI).
- Check for tapered vs. parallel threads (BSPP is parallel, BSPT and NPT are tapered).
- Compare the OD of male threads with standard charts.
What’s the best way to measure hydraulic hose fittings?
- Check the hose ID to determine the fitting size.
- Identify the thread type using a pitch gauge.
- Check the seat angle (JIC 37°, SAE 45°, or ORFS flat face).
Can I mix BSP and NPT fittings?
❌ No! The thread angles and pitches are different, causing leaks.
Need Help? Contact Hydraulics Direct Today!
At Hydraulics Direct, we provide a wide range of pipe fittings, adapters, and hose assemblies for hydraulic, industrial, and fluid transfer applications. Contact us for expert guidance in selecting the right fittings!