1/8" NPT Thread Size
Complete thread specifications for 1/8 inch NPT threads. The smallest common NPT size, ideal for pressure gauges and small instrument fittings.
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NPT threads follow ASME B1.20.1 standard with 1:16 taper
Note: This page shows 1/8" NPT dimensions. Use the dropdown above to explore other sizes.
Thread Specifications
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1/8" NPT Thread Specifications
The 1/8 inch NPT thread is the finest NPT thread with 27 TPI, requiring careful machining and assembly. Despite its small 0.4050" major diameter, it provides reliable sealing for low-flow instrumentation applications.
Key Dimensions
- Major Diameter: 0.4050" (10.29 mm)
- Minor Diameter: 0.3525" (8.95 mm)
- Threads Per Inch: 27 TPI (finest NPT thread)
- Drill Tap Size: R" (8.61 mm)
Common Applications
- Pressure gauge and vacuum gauge ports
- Small pneumatic fittings and manifolds
- Instrument air connections
- Temperature sensor ports
- Lubrication system fittings
Assembly Notes:
The 27 TPI thread is fine and delicate. Use minimal torque (5-8 ft-lbs) to avoid stripping. Apply thin coat of sealant - excess can cause hydraulic lock. Verify thread engagement with proper gauge before tightening.