ISO 228-1:2000

Overview

ISO 228-1:2000 defines requirements for pipe threads where pressure-tight joints are not made on the threads. It specifies the thread form, dimensions, tolerances and designation for parallel (non-tapered) internal and external fastening pipe threads for sizes 1/16 to 6 inclusive. These threads are intended for the mechanical assembly of fittings, cocks, valves and accessories and are not suitable as jointing threads for pressure-tight sealing on the thread surface.

Key topics and technical requirements

• Thread form and profile: Internal and external threads use the same parallel thread profile (full-form or truncated) and have defined geometric parameters (fundamental triangle height H, profile height h, crest/root radius r).
• Dimensions and sizes: Tabled thread dimensions (in millimetres) for the range 1/16 to 6 are given, including major, pitch and minor diameters and pitch values.
• Tolerances:
  • Internal thread tolerances on pitch diameter correspond to the positive deviations of ISO 7-1 (with specific differences for small sizes: 1/16, 1/8, 1/4, 3/8).
  • External threads have two tolerance classes on pitch diameter:
    • Class A: negative tolerances equivalent in value to the internal thread tolerance.
    • Class B: negative tolerances of twice the value of the respective internal thread tolerance.
• Designation and marking: Designation format includes the description, standard number and thread identifier (e.g., Pipe thread ISO 228 - G 1 1/2). Left-hand threads are suffixed LH; right-hand threads require no suffix.
• Assembly and sealing: When a pressure-tight joint is required, sealing must be achieved by compressing two tightening surfaces outside the threads and using an appropriate seal - not by relying on the thread form.
• Verification: ISO 228-2 provides recommended gauging systems and methods for verification by limit gauges.

Applications

• Use ISO 228-1 for specifying fastening pipe threads in mechanical assemblies where threads are for locating/holding components (fittings, valves, taps, instrument connections).
• Appropriate where threaded parts will be sealed with separate gaskets, O-rings or gasketed faces rather than by thread engagement.
• Useful for manufacturers, product designers and technical specification writers creating pipe fittings and accessories that require standardized parallel threads.

Who uses this standard

• Mechanical designers and engineers specifying thread interfaces
• Pipe and valve manufacturers, fittings and accessory suppliers
• Quality assurance, inspection and metrology teams (thread gauging)
• Procurement and regulatory compliance specialists

Related standards

• ISO 7-1 - pipe threads where pressure-tight joints are made on the threads (jointing/tapered threads)
• ISO 228-2 - verification by means of limit gauges (gauging and inspection methods)

Keywords: ISO 228-1, pipe threads, parallel threads, thread dimensions, tolerances, designation, fastening threads, pressure-tight, ISO 7-1, thread gauging.