1. Why Every Millimeter Matters in Pipe Connections
In the piping industry, there’s no room for "close enough." We specialize in supplying ASTM A105N & 316L Threaded Pipe Flanges, ensuring that every dimension adheres strictly to ASME B16.5 (the American standard for pipe flanges and flanged fittings). Whether it is the Nominal Pipe Size (NPS) or the Thread Pitch, precision is what keeps a high-pressure system from becoming a safety hazard.
Precision Benchmarks: ASME B16.5 Dimensional Tolerances
| Inspection Item | Specification | ASME B16.5 Tolerance | Our Factory Control |
| Outside Diameter | ≤ NPS 10 | ±2.0 mm | ±1.0 mm |
| Thread Taper | All Sizes (NPT) | 1 : 16 (±0.06) | 1 : 16 (±0.03) |
| Thickness | ≤ NPS 18 | +3.0/ - 0 mm | +1.5/ -0 mm |
| Bolt Hole Circle | All Sizes | ±1.5 mm | ±0.8 mm |
| Nut Bearing Surface | All Sizes | Parallelism ≤ 1° | Parallelism ≤ 0.5° |
2. Decoding the Specs: From NPS to Class Ratings
Understanding the jargon is key to a perfect fit. NPS (Nominal Pipe Size) refers to the standardized outside diameter, while the Class Rating (such as Class 150 or 300) defines the maximum pressure the flange can handle. Our ASTM A105N Carbon Steel and 316L Stainless Steel flanges are machined to handle the wall thickness requirements of various Pipe Schedules (like Sch 40 or Sch 80).
Table 1: Common Threaded Flange Dimensions (Class 150 - Reference)
| NPS (Size) | Outside Diameter (mm) | Hub Diameter (mm) | Bolt Hole Circle (mm) |
| 1/2" | 90 | 30 | 60.3 |
| 1" | 110 | 49 | 79.4 |
| 2" | 150 | 78 | 120.7 |
| 4" | 230 | 135 | 190.5 |
3. Thread Geometry: NPT vs. BSPT Standards
The heart of a Screwed Flange is the thread itself. NPT (National Pipe Thread) is the North American standard with a tapered thread that provides a metal-to-metal seal. Alternatively, BSPT (British Standard Pipe Taper) is widely used in Europe and Asia. We use L1/L2 thread gauges to ensure the Taper Angle (1°47') is flawless, preventing the "thread galling" that ruins standard connections.
Table 2: Thread Comparison & Tolerance Data
| Thread Type | Angle | Taper | Standard |
| NPT | 60° | 1:16 | ASME B1.20.1 |
| BSPT (Rc) | 55° | 1:16 | ISO 7 / EN 10226 |
Threaded Flange Weight Comparison Table: Standard: ASME B16.5 | Material: ASTM A105N / 316L
| Nominal Pipe Size (NPS) | Class 150 (lb) | Class 150 (kg) | Class 300 (lb) | Class 300 (kg) |
| 1/2" | 2.0 | 0.9 | 3.0 | 1.4 |
| 3/4" | 2.0 | 0.9 | 3.5 | 1.6 |
| 1" | 2.5 | 1.1 | 4.5 | 2.0 |
| 1-1/4" | 3.0 | 1.4 | 6.0 | 2.7 |
| 1-1/2" | 4.0 | 1.8 | 8.0 | 3.6 |
| 2" | 5.0 | 2.3 | 8.5 | 3.9 |
| 2-1/2" | 9.0 | 4.1 | 12.5 | 5.7 |
| 3" | 10.5 | 4.8 | 16.5 | 7.5 |
| 4" | 16.5 | 7.5 | 28.0 | 12.7 |
Getting the dimensions right on the order sheet is only half the battle; the real test happens when your crew starts threading these onto the pipe. Even a flange machined to a perfect ASME B16.5 standard can be ruined by improper torque or a lack of thread sealant during the initial bite. Precision specs are designed to make your life easier on-site, but there’s a specific "knack" to getting that 100% leak-free seal the first time. To make sure your project doesn't get slowed down by common assembly errors, [check out our Professional Threaded Flange Installation Guide] for the step-by-step best practices.
