What’s the relationship between ISO 261, 724, and 965?

ISO 261 defines the plan; ISO 724 gives basic dimensions; ISO 965 provides tolerances and limits.

Where do I find trapezoidal (Tr) thread data?

See ISO 2901–2904 for profiles, plan, tolerances, and basic dimensions.

Which standard covers gauges for ISO metric threads?

ISO 1502—manufacture and use of gauges for checking ISO metric screw threads.

What does ISO 68 define in screw threads?

ISO 68 defines the basic profile for ISO screw threads. Part 1 covers metric screw threads (M), and Part 2 covers inch screw threads. Other ISO standards build on this base profile to define sizes and tolerances.

Which ISO standard defines metric screw thread tolerances?

ISO 965 specifies the tolerances, limits of size, and deviations for general-purpose metric screw threads. It has multiple parts covering external, internal, and special cases such as galvanized threads.

What is the difference between ISO and ASME screw thread standards?

ISO standards are used internationally and focus mainly on metric and inch screw threads. ASME B1 standards are primarily used in the United States and cover Unified, Acme, Buttress, and pipe threads. Both ensure compatibility but apply to different markets.

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ISO Screw Thread Standards: Complete List & Summaries

A practical index of key ISO screw thread standards with one-line summaries: basic profiles (ISO 68), metric/inch plans & sizes (ISO 261/262/263/724/725), tolerances (ISO 965), trapezoidal (ISO 2901–2904), miniature (ISO 1501), gauges (ISO 1502), and measuring wires (ISO 16239).

ISO screw thread standards define the geometry, tolerances, and inspection practices for metric and inch screw threads used worldwide in fasteners, machinery, and precision components. They provide engineers and manufacturers with a uniform reference to ensure compatibility and interchangeability of threaded parts.

The International Organization for Standardization (ISO) publishes these standards in the ISO 68, ISO 261, ISO 262, ISO 724, and ISO 965 series, among others. Together, they cover the basic thread profile, the diameter–pitch combinations, limits and tolerances, as well as gauges and gaging methods. Additional documents define trapezoidal screw threads, miniature screw threads, and thread terminology.

In practice, these ISO standards are essential for:

Designing bolts, nuts, and threaded fasteners with consistent fit.
Defining tolerances for critical assemblies in automotive, aerospace, and machinery industries.
Ensuring accurate inspection with standardized gauges and measuring wires.
Supporting global trade by harmonizing screw thread specifications across countries.

This page lists the most important ISO standards for screw threads with publication year, scope, and a short summary to help engineers quickly locate the correct reference. For comparison, see also our ASME B1 screw thread standards.

Standard	Name	Summary
ISO 68-1:1998	ISO general-purpose screw threads — Basic profile — Part 1: Metric	Defines the basic profile for ISO metric threads (M).
ISO 68-2:1998	ISO general-purpose screw threads — Basic profile — Part 2: Inch	Defines the basic profile for ISO inch threads.
ISO 261:1998	ISO general-purpose metric screw threads — General plan	Defines ISO metric thread plan; links to basic dimensions (ISO 724) and tolerances (ISO 965).
ISO 262:1998	ISO general-purpose metric screw threads — Selected sizes	Preferred sizes for screws/bolts/nuts from 1 to 64 mm.
ISO 263:1973	ISO inch screw threads — General plan & selection (0.06–6 in)	Inch series plan and designations (non-pipe threads).
ISO 724:1993	ISO general-purpose metric screw threads — Basic dimensions	Basic dimensions for ISO metric threads (per ISO 68-1/261).
ISO 725:2009	ISO inch screw threads — Basic dimensions	Basic dimensions for ISO inch threads (per ISO 68-2/263).
ISO 965-1:2013	ISO metric screw threads — Tolerances — Part 1: Principles & basic data	Principles and basic data for ISO metric thread tolerances.
ISO 965-2:1998	ISO metric screw threads — Tolerances — Part 2: Limits of sizes (general purpose)	Limits of sizes for external/internal threads (medium quality).
ISO 965-3:1998	ISO metric screw threads — Tolerances — Part 3: Deviations for constructional threads	Deviations for constructional uses (per ISO 261; ISO 68-1 profile).
ISO 965-4:1998	ISO metric screw threads — Tolerances — Part 4: Hot-dip galvanized external threads	Limits for galvanized external threads mating with H or G internal threads.
ISO 965-5:1998	ISO metric screw threads — Tolerances — Part 5: Internal threads to mate with galvanized externals	Limits for internal threads to mate with tolerance h external threads before galvanizing.
ISO 2901:1993	ISO metric trapezoidal screw threads — Basic & maximum material profiles	Defines basic and maximum material profiles for Tr threads.
ISO 2902:1977	ISO metric trapezoidal screw threads — General plan	Series of diameter/pitch combinations for trapezoidal threads.
ISO 2903:1993	ISO metric trapezoidal screw threads — Tolerances	Tolerance system for Tr threads (lead screws & special axial displacement not covered).
ISO 2904:1977	ISO metric trapezoidal screw threads — Basic dimensions	Basic dimensions for Tr threads (per ISO 2902 plan).
ISO 1501:2009	ISO miniature screw threads	Profiles, diameter-pitch sets, dimensions and tolerances for 0.3–1.4 mm miniature threads.
ISO 1502:1996	ISO general-purpose metric screw threads — Gauges & gauging	Manufacture and use of gauges for checking ISO metric threads (external & internal).
ISO 5408:2009	Screw threads — Vocabulary	Fundamental terminology for symmetrical/unsymmetrical, cylindrical/tapered threads.
ISO 5864:1993	ISO inch screw threads — Allowances & tolerances	System of allowances/tolerances for standard inch thread series (0.06–6 in).
ISO 16239:2013	Metric series wires for measuring screw threads	Material, nominal diameters, tolerances, and designation for thread-measuring wires.

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

FAQ — ISO Screw Thread Standards

What’s the relationship between ISO 261, 724, and 965?: ISO 261 defines the plan; ISO 724 gives basic dimensions; ISO 965 provides tolerances and limits.
Where do I find trapezoidal (Tr) thread data?: See ISO 2901–2904 for profiles, plan, tolerances, and basic dimensions.
Which standard covers gauges for ISO metric threads?: ISO 1502—manufacture and use of gauges for checking ISO metric screw threads.
What is the difference between ISO and ASME screw thread standards?: ISO standards are used internationally and focus mainly on metric and inch screw threads. ASME B1 standards are primarily used in the United States and cover Unified, Acme, Buttress, and pipe threads. Both ensure compatibility but apply to different markets.
Which ISO standard defines metric screw thread tolerances?: ISO 965 specifies the tolerances, limits of size, and deviations for general-purpose metric screw threads. It has multiple parts covering external, internal, and special cases such as galvanized threads.
What does ISO 68 define in screw threads?: ISO 68 defines the basic profile for ISO screw threads. Part 1 covers metric screw threads (M), and Part 2 covers inch screw threads. Other ISO standards build on this base profile to define sizes and tolerances.