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NPS Thread Pitch Chart
NPS stands for National Pipe Straight. NPS threads are part of the American pipe thread system and are defined under the ASME B1.20.1 standard. Unlike NPT threads, NPS threads are straight (parallel) threads rather than tapered. NPS threads use a 60° thread profile with flattened peaks and valleys. Because NPS threads do not create a seal through thread interference, sealing is typically achieved using gaskets, O-rings, washers or other sealing methods. NPS threads are commonly used in pipe fittings, mechanical components, electrical conduit and industrial applications.
| Diameter | TPI | Drill Size (mm) |
|---|---|---|
| 1/8" | 27 | 8.9 mm |
| 1/4" | 18 | 11.5 mm |
| 3/8" | 18 | 15.0 mm |
| 1/2" | 14 | 18.5 mm |
| 3/4" | 14 | 24.0 mm |
| 1" | 11.5 | 30.0 mm |
| 1-1/4" | 11.5 | 39.0 mm |
| 1-1/2" | 11.5 | 45.0 mm |
| 2" | 11.5 | 56.50 mm |
NPS vs NPT Threads
Although NPS and NPT share the same 60° thread form, they are fundamentally different and not interchangeable for sealing applications.
NPS (National Pipe Straight)
- Parallel thread design
- Same basic thread profile as NPT
- Requires a separate sealing method
- Used where alignment, assembly and disassembly are important
NPT (National Pipe Taper)
- Tapered thread design
- Creates a seal through thread engagement
- Commonly used for pressure-tight pipe connections
How to Read the NPS Thread Chart
The NPS Thread Chart above provides a quick reference for National Pipe Straight thread sizes. Each column shows essential information for engineers, machinists, hydraulic technicians and maintenance professionals:
- Diameter – The nominal pipe size in imperial measurements
- TPI – Threads Per Inch, indicating thread pitch
- Drill Size (mm) – The recommended drill size for tapping NPS threads
Pipe thread sizes are based on nominal pipe sizing and do not directly match the measured outside diameter of the thread. This reference chart helps you select the correct drill bit and understand thread specifications for accurate machining and assembly.
Common Applications
NPS threads are found across a wide range of industrial and mechanical applications, including:
- Pipe fittings and connectors
- Mechanical assemblies and equipment
- Electrical conduit systems
- Industrial equipment and machinery
- Pumps and valves
- Hydraulic systems
- Manufacturing equipment
- Maintenance and repair work
Frequently Asked Questions
What does NPS stand for?
NPS stands for National Pipe Straight, a thread standard defined under ASME B1.20.1.
What is the difference between NPS and NPT?
NPS threads are parallel (straight), while NPT threads are tapered. NPT creates a seal through thread engagement, whereas NPS requires a separate sealing method such as gaskets or O-rings.
Are NPS threads tapered?
No. NPS threads are parallel (straight) threads. If you need tapered threads for pressure-tight sealing, NPT is the appropriate choice.
Do NPS threads require thread sealant?
NPS threads do not create a seal through thread interference alone. Sealing is achieved using gaskets, O-rings, washers or other mechanical sealing methods rather than thread sealant.
Are NPS and BSP threads interchangeable?
No. NPS and BSP (British Standard Pipe) are different thread standards with different dimensions and profiles. They are not interchangeable.
How do I identify an NPS thread size?
Use the NPS Thread Chart above to match your nominal pipe size with the corresponding TPI and drill size. Measure the nominal diameter and count the threads per inch to confirm the size.