Pipe Thread
Tapered and parallel pipe-thread dimensions, tolerances, and gauging.
ASME B1.20.1
ASMEPipe Threads, General Purpose (NPT)
Specifies dimensions, tolerances, and gauging methods for general-purpose inch taper pipe threads (NPT) in sizes 1/16″ through 12″ NPS, along with straight pipe thread variants (NPSC, NPSM, NPSL, NPTR). NPT threads achieve mechanical engagement through a 60° taper form at a rate of ¾ in/ft on diameter, but always require a compatible thread sealant to achieve a leak-tight joint — the thread form alone does not seal.
ASME B1.20.3
ASMEDryseal Pipe Threads (NPTF)
Specifies dimensions, tolerances, and gauging for dryseal (NPTF) inch pipe threads in sizes 1/16″ through 2″ NPS, where a pressure-tight joint is achieved by metal-to-metal contact of the thread crests and roots — no thread sealant is required. The tighter crest/root tolerances compared to NPT force interference that closes the helical leak path inherent in the standard NPT form.
ISO 7-1
ISOPipe Threads Where Pressure-Tight Joints Are Made on the Threads (R/Rc/Rp)
Specifies dimensions, tolerances, and gauging for the BSPT (British Standard Pipe Taper) family of pipe threads — taper external (R), taper internal (Rc), and parallel internal (Rp) — where the pressure-tight joint is achieved on the thread flanks using a 55° Whitworth form and a 1:16 taper on diameter. Sizes range from R 1/16 through R 6. A thread sealant is normally required. This is the dominant pipe thread standard in Europe, Asia-Pacific, and on internationally sourced equipment.
ISO 228-1
ISOPipe Threads Where Pressure-Tight Joints Are Not Made on the Threads (G / BSPP)
Specifies dimensions, tolerances, and tolerance classes for parallel (straight) pipe threads designated "G" — the BSPP (British Standard Pipe Parallel) family — in sizes G 1/16 through G 6. The threads provide mechanical retention only; the pressure-tight seal is always achieved by a separate sealing element (O-ring, bonded washer, or machined seating face). This is the dominant parallel pipe thread standard in Europe, Asia-Pacific, and on hydraulic and pneumatic equipment worldwide.