The Essential Guide to Threaded Flange Sizes: Measurement and Charts
Selecting the correct threaded pipe flange size is critical for the safety and integrity of your piping system. Whether you are replacing a worn-out part or designing a new system, understanding how to read a threaded flange size chart and how to take field measurements is a fundamental skill.
In this guide, we provide a complete breakdown of dimensions for Class 150 threaded flanges according to ANSI B16.5 standards.
How to Measure a Threaded Pipe Flange? (Step-by-Step)
If you are at a job site in Texas or Queensland without a spec sheet, follow these four steps to identify your flange:
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Measure the Outer Diameter (OD): Use a caliper to measure the total width of the flange across the center.
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Count the Bolt Holes: Standard sizes usually have 4, 8, 12, or more holes.
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Measure the Bolt Circle (BC): This is the distance from the center of one bolt hole to the center of the opposite hole. This is the most critical measurement for alignment.
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Identify the Thread Type (NPT vs BSP): * NPT (USA Standard): Threads are tapered.
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BSP/BSPT (AU/UK Standard): Often found in Australian water and gas projects.
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Pro Tip: Use a thread pitch gauge to confirm before ordering.
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H2: ANSI B16.5 Class 150 Threaded Flange Size Chart
| Nominal Pipe Size (NPS) | Outer Diameter (OD) | Bolt Circle (BC) | Number of Holes | Bolt Hole Dia |
| 1" (1 inch) | 4.25" | 3.12" | 4 | 0.62" |
| 2" (2 inch) | 6.00" | 4.75" | 4 | 0.75" |
| 3" (3 inch) | 7.50" | 6.00" | 4 | 0.75" |
| 4" (4 inch) | 9.00" | 7.50" | 8 | 0.75" |
(Note: For a full PDF chart from 1/2" to 24", please contact our support team.)
Why Precision Matters for Tapped Flanges
A tapped flange (another name for a threaded flange) relies on the precision of the internal threads. If the thread pitch is slightly off (e.g., trying to force an NPT pipe into a BSP flange), you risk catastrophic leaks or galling the metal.
Looking for High-Quality Threaded Flanges?
We supply a full range of threaded flanges in Carbon Steel A105 and Stainless Steel 316L. With stock available in the USA (FL, CA, TX) and Australia (Sydney, QLD), we can deliver the exact size you need within days.
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