1/2" NPT Thread Size
Complete thread specifications for 1/2 inch NPT (National Pipe Taper) threads. One of the most common pipe thread sizes for plumbing, hydraulics, and pneumatic applications.
Select NPT Thread Size
NPT threads follow ASME B1.20.1 standard with 1:16 taper
Note: This page shows 1/2" NPT dimensions. Use the dropdown above to explore other sizes.
Thread Specifications
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1/2" NPT Thread Specifications
The 1/2 inch NPT thread is one of the most widely used pipe thread sizes in industrial and residential applications. With a major diameter of 0.8400" and 14 threads per inch, it provides excellent sealing capability for pressures up to 1000+ PSI when properly assembled.
Key Dimensions
- Major Diameter: 0.8400" (21.34 mm) - Matches 1/2" Schedule 40 pipe OD
- Minor Diameter: 0.7665" (19.47 mm) - Root diameter at thread valley
- Pitch Diameter: 0.8031" (20.40 mm) - Effective sealing diameter
- Threads Per Inch: 14 TPI - Thread density for 1/2" size
- Drill Tap Size: 23/32" (18.26 mm) - For 75% thread engagement
Common Applications
- Residential Plumbing: Water supply lines, gas lines, water heaters, boiler connections
- Pneumatic Systems: Compressed air distribution, air compressor fittings, air tool connections
- Hydraulic Systems: Low to medium pressure hydraulic lines, pressure gauges, valve connections
- HVAC: Refrigerant lines (with proper sealing), condensate drains, pressure switches
- Industrial: Process piping, instrumentation connections, chemical transfer (with compatible materials)
Threading & Assembly Guidelines
Step-by-Step Assembly:
- Clean threads: Remove debris, old sealant, and metal shavings from both male and female threads
- Apply sealant: Use Teflon tape (3-4 wraps) or pipe dope on male threads only. Never use both together.
- Hand-tighten: Thread connection by hand for 4 complete turns until snug
- Wrench-tighten: Use wrench to tighten an additional 2 turns (approximately 1-1/2 turns total from hand-tight)
- Verify alignment: Ensure fitting is oriented correctly before final tightening
- Pressure test: Test at operating pressure to verify leak-free seal
Torque Specification: Typical torque range for 1/2" NPT is 15-20 ft-lbs for steel fittings. Brass fittings require less torque (10-15 ft-lbs) to avoid cracking. Always follow manufacturer recommendations.
Material Compatibility
| Material | Max Pressure | Temperature Range | Applications |
|---|---|---|---|
| Steel | 1000+ PSI | -20°F to 400°F | High pressure water, steam, oil |
| Stainless | 1500+ PSI | -100°F to 800°F | Corrosive fluids, food grade, marine |
| Brass | 600 PSI | 32°F to 250°F | Potable water, low pressure gas |
| PVC | 150 PSI | 40°F to 140°F | Drainage, irrigation (not potable) |
Common Issues & Solutions
Leaking Connection
Causes: Insufficient sealant, cross-threading, over-tightening (cracked fitting), incompatible thread types (NPT vs NPS).
Solution: Disassemble, inspect for damage, clean threads, apply fresh sealant, reassemble with proper tightening sequence.
Stripped Threads
Causes: Over-tightening, misaligned threading, soft materials (brass, aluminum) with excessive torque.
Solution: Replace damaged fitting. Use thread repair inserts (HeliCoil) for female threads in soft materials. Use torque wrench to prevent recurrence.
Difficult Disassembly
Causes: Sealant has hardened, corrosion, galling (stainless on stainless).
Solution: Apply penetrating oil, heat fitting moderately, use proper size wrenches to avoid rounding. For future installations, use anti-seize compound on stainless threads.