ISO 965 Metric Screw Thread Tolerances

ISO 965 specifies the tolerance system for ISO metric screw threads with a 60° profile. The basic profile of these threads is defined in our ISO 68-1 thread profile page, while the ISO 965 series establishes the limits and fits applied to internal and external threads. The standard series covers the principles and basic data used to establish thread tolerances, together with the limits of sizes for internal and external threads. ISO 965-1 defines the tolerance system and selection of tolerance classes, while ISO 965-2 provides the limits of sizes for commonly used metric screw threads.

ISO 965-1: Principles and Basic Data

ISO 965-1 establishes the principles and basic data for the ISO system of limits and fits for metric screw threads. It defines the tolerance positions, tolerance grades and tolerance classes used for internal and external threads, and provides the basis for selecting suitable thread tolerances according to thread size and engagement length.

Tolerance Position

The tolerance position defines the location of the tolerance zone relative to the basic profile of the thread. For internal threads, the commonly used positions are G and H, while external threads use e, f, g and h. The position is identified by a letter: capital letters are used for internal threads and lower-case letters for external threads.

Recommended Tolerance Classes

These tolerance classes are widely used for general-purpose ISO metric screw threads. Other tolerance classes may be selected when specific requirements for fit, manufacturing conditions or thread engagement apply. The lengths of thread engagement are classified into one of three groups: short (S), normal (N) or long (L).

Recommended tolerance classes for internal threads

Recommended tolerance classes for external threads

ISO965-2

ISO 965-2 specifies the limits of sizes for the pitch and crest diameters of ISO general purpose metric screw threads. It provides the dimensional limits derived from the tolerance system established in ISO 965-1, covering both internal and external threads. For commonly used metric fastening threads, ISO 965-2:2024 applies to tolerance classes 6H and 6g for thread sizes from M1.6 to M100, with 5H and 6h specified for sizes from M1 to M1.4. These limits define the allowable size range of the thread and provide the dimensional basis for controlling thread production and inspection.

ISO965-2 Limits of sizes for internal threads

Internal threads

Tolerance quality: Medium

Length group of thread engagement: Normal

Tolerance class: 5H for screw threads with nominal diameters up to and including 1,4 mm;d -6H for screw threads with nominal diameters over 1,4 mm.

ISO965-2 Limits of sizes for external threads

External threads

Tolerance quality: Medium

Length group of thread engagement: Normal

Tolerance class: 6h for screw threads with nominal diameters up to and including 1,4 mm;d 6g for screw threads with nominal diameters over 1,4 mm.