National Pipe Thread Fuel (NPTF)
- Thread conforms to ANSI B1.20.3
- Physically interchangeable with NPT but has modified
threads for better pressure tight sealing
- Tapered thread profile seals by metal to metal interference fit,
usually requires sealing compound for pressure tight
connections
- Pitch and diameter are measured in inches
- Taper angle is 0.75≤ per foot or 1° 47¢
- Thread angle is 60°
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Straight Thread O-Ring (SAE)
- Thread conforms to ISO 263 and ANSI B1.1 Unified
- Port conforms to ISO 11926 and SAE J1926
- Commonly called straight thread O-ring fittings
- Pitch and diameter are measured in inches, 1Z\zn-12 UN-2B
- Threads are parallel and requires O-ring for pressure tight
connection
- Thread angle is 60°
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British Standard Pipe Tapered (BSPT)
- Thread conforms to ISO 7
- Pitch and diameter are measured in inches, e.g. G3/8-19
- Tapered thread profile seals by metal to metal interference fit,
usually requires sealing compound for pressure tight
connection
- Taper angle is 1° 47¢, the same as NPT(F)
- Thread angle is 55°
- Not interchangeable with NPT(F)
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British Standard Pipe Parallel (BSPP)
- Thread conforms to ISO 228-1
- Port conforms to ISO 1179
- Pitch and diameter measured in inches, e.g. G1/4-19
- Parallel threads require O-ring, crush washer, gasket or
metal to metal seal between connections for pressure tight
connection
- Thread angle is 55º
- Not interchangeable with SAE or NPT(F)
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Metric Straight Thread O-Ring
- Thread conforms to ISO 261
- Port conforms to ISO 6149 and SAE J2244
- Pitch and diameter measured in millimeters, e.g. M22 x 1.5
- Parallel threads require O-ring for pressure tight connection
- Thread angle is 60°
- Easily identified by raised ridge on female port counterbore
- Not interchangeable with SAE or BSPP
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