Thread tolerance class

Illustrated explanation

Count full-form engagement at the actual interface

6Thread tolerance class
Count full-form engagement at the actual interfaceCallout 1: External thread. Callout 2: Internal thread. Callout 3: Engaged length. Callout 4: Total thread length. Callout 5: Incomplete transition. Callout 6: Permitted thread variation. The external part and internal part must overlap in usable thread turns. Total threaded length can include runout and incomplete turns; permitted fit also depends on tolerance class. Current term: Thread tolerance class, callout 6. 1External thread 2Internal thread 3Engaged length 4Total thread length 5Incomplete transition 6Specified position + gradePermitted thread variation
  1. External thread

    The profile lies on the outside of the fitting. Confirm its full designation, coating condition and usable length.

  2. Internal thread

    The thread lies inside the receiving hole or component. Its standard, fit and usable depth must match the external part.

  3. Thread engagement

    The arrow shows the overlapping region of the mating threads. Exclude unusable turns and account for the actual load and materials.

  4. Thread length

    The overall threaded portion is a dimension of the fitting. It can exceed the full-form length available to the mating part.

  5. Thread runout

    The profile becomes incomplete near the shoulder. Leave relief space and do not count this transition as full engagement.

  6. Thread tolerance classThis term

    The band represents permitted dimensional variation. Complete classes and coating conditions must be specified for each mating part.

The external part and internal part must overlap in usable thread turns. Total threaded length can include runout and incomplete turns; permitted fit also depends on tolerance class.

Conceptual sections. No minimum turn count, engagement length or tolerance class is specified by this figure.

ReferencesISO 965-1:2026 — General-purpose metric screw-thread tolerancesISO 7-1:1994 — Pipe threads where pressure-tight joints are made on the threadsISO 228-1:2000 — Pipe threads where pressure-tight joints are not made on the threadsIEC 60423:2007 — Conduit diameters and threads for conduits and fittingsIEC 60079-14 — Electrical installations design, selection and installationIEC 62444:2010 — Cable glands for electrical installationsISO 5408:2009 — Screw threads — Vocabulary