NPT (National Pipe Taper)

NPT is a U.S. tapered pipe thread standard (ANSI/ASME B1.20.1). NPT threads seal by interference and thread deformation — use thread sealant or tape for gas-tight joints.

• Identification: Tapered threads, measured by nominal pipe size (e.g., 1/8", 1/4", 1/2").
• Sealing: Thread sealant or PTFE tape.
• Common uses: Plumbing, air and fuel lines, adapters.

BSP (British Standard Pipe) — BSPT / BSPP

BSP comes in tapered (BSPT) and parallel (BSPP) forms. BSPT seals similarly to NPT (tapered), while BSPP often relies on an O-ring or washer for sealing when used with a mating port.

AN / JIC / Flare (37° and 45°)

AN (Army-Navy) fittings use a 37° flare seat (often called JIC in hydraulic contexts). Metric flare and SAE flares may use a 45° seat (common on brake lines and automotive tubing).

• Identification: Flared tube end with matching flare nut and male fitting.
• Sealing: Metal-to-metal flare face (37° or 45°) — avoid over-tightening; use proper flare tools.
• Common uses: High-pressure hydraulics, fuel lines (AN), brake lines (45° SAE).

ORB (O-Ring Boss)

ORB fittings use a straight thread with a recessed port containing an O-ring for sealing. Threads themselves do not seal — the O-ring does.

• Identification: Parallel threads with a hex shoulder and a visible O-ring in the female port.
• Sealing: Elastomeric O-ring; ensure O-ring material compatibility.
• Common uses: Hydraulic ports on pumps, valves, and manifolds.

Metric Threads (ISO)

Metric threads follow the ISO metric standard (M# × pitch). Use appropriate thread gauges or measure major diameter and pitch to identify.

Assembly Best Practices

• Clean threads and mating surfaces.
• Use proper sealants where required (PTFE tape for NPT, thread paste for high-pressure gas).
• Do not reuse damaged ferrules or flares; replace if deformed.
• Torque to manufacturer specs — avoid over-tightening.

Quick AN Size Reference Table