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ASME Screw Thread Standards (B1 Series): Complete List

A practical index of ASME B1 screw thread standards with one-line summaries for quick selection: UN/UNR/UNJ, Acme & Stub Acme, Buttress, Metric M & MJ, Pipe (NPT, Dryseal), gaging, and rounding practices.

Tip: you can search by number, name, or keywords.

Related: UNC thread charts, Tap drill size calculator, Thread tolerance calculator. Acme thread calculator.

Standard Pages Year Name Summary
B1.1-2003 188 2003 Unified Inch Screw Threads (UN & UNR Thread Form) Defines form, series, classes, allowance, tolerances, and designation for unified screw threads.
B1.2-1983 179 1983 Gages and Gaging for Unified Inch Screw Threads Specifications and dimensions for thread gages and measuring equipment for UN/UNR threads.
B1.3-2007 20 2007 Screw Thread Gaging Systems for Dimensional Acceptability — Inch & Metric (UN, UNR, UNJ, M, MJ) Gaging systems for determining acceptability of UN/UNR/UNJ and metric M/MJ threads (internal & external).
B1.5-1997 124 1997 Acme Screw Threads General purpose and centralizing Acme threads (single-start; also guidance for multiple-start if suitable).
B1.7-2006 36 2006 Screw Threads: Nomenclature, Definitions, and Letter Symbols Uniform practice for screw thread terms and symbols for drawings, tables, and formulae.
B1.8-1988 30 1988 Stub Acme Screw Threads Coarse-pitch, shallow depth threads for special applications constrained by mechanics or metallurgy.
B1.9-1973 21 1973 Buttress Inch Screw Threads (7°/45°), 0.6p Basic Height Buttress form threads for unidirectional loads; geometry and engagement height specified.
B1.10M-2004 24 2004 Unified Miniature Screw Threads Miniature threads 0.30–1.40 mm; extends below ISO/Unified series that start at 1.6 mm.
B1.11-1958 (rev. 2011) 9 2011 Microscope Objective Thread Mounting thread for objective assemblies to microscope bodies/turrets.
B1.12-1987 56 1987 Class 5 Interference-Fit Thread Plastic-flow interference-fit (Class 5) threads, modified National form, coarse series, 0.250–1.500 in.
B1.13M-2005 16 2005 Metric Screw Threads: M Profile General metric 60° symmetrical M-profile (ISO 68-1 base) — form and general data.
B1.15-1995 72 1995 Unified Inch Screw Threads (UNJ Thread Form) UNJ profile, designations, diameter-pitch series (0.600–6.000 in), limits and tolerances.
B1.16M-1984 164 1984 Gages and Gaging for Metric M Screw Threads Specifications/dimensions for gages and measuring equipment for M series metric threads.
B1.20.1-2013 40 2013 Pipe Threads, General Purpose, Inch Dimensions and gaging for NPT, NPSC, NPTR, NPSM, NPSL series.
B1.20.2M-2006 28 2006 Pipe Threads, 60° General Purpose (Metric) Metric conversion of ASME B1.20.1 (NPT) for general purpose pipe threads.
B1.20.3-1976 19 1976 Dryseal Pipe Threads, Inch Modified American pipe threads designed to seal pressure-tight joints without sealing compounds.
B1.20.5-1991 59 1991 Gaging for Dryseal Pipe Threads — Inch Practical inspection methods and commonly used gages for production evaluation of Dryseal pipe threads.
B1.20.7-1991 14 1991 Hose Coupling Screw Threads, Inch Threads for hose couplings, valves, nozzles, and fittings (½ to 4 in common sizes).
B1.21M-1997 64 1997 Metric Screw Threads: MJ Profile MJ profile for 1.6–200 mm; designations, diameter/pitch series, limits and tolerances.
B1.22M-1985 136 1985 Gages and Gaging for MJ Metric Screw Threads Specifications/dimensions for gages used on MJ metric threads and related measuring equipment.
B1.30-2002 32 2002 Screw Threads: Standard Practice for Calculating & Rounding Dimensions Uniform practices for calculating and rounding numeric values for inch/metric screw thread design dimensions.

Note: Titles, years, and short scopes are provided to help engineers pick the correct document; always consult the latest ASME publication for design.

FAQ — ASME B1 Screw Thread Standards

What’s the difference between UN, UNR, and UNJ?
UN is the base unified form; UNR specifies a rounded root on external threads; UNJ includes a larger root radius to improve fatigue strength (common in aerospace).
When should I use Dryseal (B1.20.3) vs. NPT (B1.20.1)?
Dryseal is designed to seal without compound; general NPT often uses sealant. Follow the governing standard for your application and pressure/medium.
Which standard covers gaging for metric M threads?
B1.16M (M series) and B1.22M (MJ series) cover gages and gaging requirements for metric profiles.