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The Hubs Standard

Threads and Tolerances

Threads

Types and notation

We offer four types of standard threads

  • UNC and UNF

    • UTS standard: ASME/ANSI B1.1 – 2019

  • Metric

  • NPT

    • NPT (National Pipe thread) standard: ANSI/ASME B1.20.1

Additional points to consider:

  • We tolerate other types of threads such as NPS, NPTS, STI, BSP, although not all our suppliers will accept them, therefore your order may take longer to be sourced.

  • We do not accept ACME or Thorlabs threads.

Threads need to be called out in the "edit part" modal of your draft quote. It takes precedence over information present in the technical drawing and cannot contradict it. If threads are needed, you will need to attach a technical drawing with more details.

Thread tolerances

Unless specified on the drawing, metric threads tolerances should follow the ISO 965-1 standard. The standard thread tolerances are used for external and internal threads: 6H for internal threads and 6g for external threads.

The absence of tolerance class designation means that tolerance quality “medium” with the following tolerance classes will be used:

Internal threads

  • 5H for threads up to and including M1,4

  • 6H for threads M1,6 and larger

GO-NOGO gauge for internal thread M24 6H
Tolerance classes for internal threads

External threads

  • 6h for threads up to and including M1,4

  • 6g for threads M1,6 and larger

GO-NOGO gauge for internal thread M12 6g
Tolerance classes for external threads

UN Threads Tolerances:

Unless specified on the drawing, UN threads tolerances should follow the ASME B1.1-2003 standard. The standard thread tolerances are used as for external and internal threads: 2A for external threads and 2B for internal threads.

Tolerances

Linear, angular dimensions and geometrical tolerances

We have two categories of tolerances: "GENERAL TOLERANCE" and "TIGHTER TOLERANCES".

  • " General tolerance" is the tolerance across the part if nothing is indicated on a technical drawing.

    • For metals, the standard is

      ISO-2768 fH (fine) (see table below)

    • For plastics, the standard is

      ISO-2768 mK (medium) (see table below)

  • " Tighter tolerances": if tolerances tighter than ISO-2768 are needed, it can be requested when building a quote. It also needs to be specified in a technical drawing in order to indicate exactly which features are concerned.

You will be asked about tolerances when building your quote: tolerances are selected in the 'edit part' modal of your draft quote. It takes precedence over information present in the technical drawing and cannot contradict it.

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