ISO 7226:1988

Overview

ISO 7226:1988 specifies the general dimensions and marking for hexagonal die nuts (hexagonal dies) used for hand threading. This second edition (1988) supersedes ISO 7226:1985 with a minor revision. The standard covers hexagonal die nuts for a range of thread systems: ISO metric (coarse and fine), ISO inch (UNC/UNF), pipe threads (series R and G), and non-preferred series (BSW, BSF, BA). It was prepared by ISO/TC 29 (Small tools).

Key topics and requirements

• Scope and applicability: Dimensional rules for hexagonal die nuts intended for manual threading, including groups of threaded diameters and corresponding dies.
• Dimensional tables: Two main tables define dimensional characteristics:
  • Table 1 - Hexagonal die nuts for metric and inch threads (excluding tapered pipe series R).
  • Table 2 - Hexagonal die nuts for tapered pipe threads, series R (gives approximate base diameters, pitch and cut length E).
• Length and profile parameters: Specifies machined (cut) lengths and related size groups; the standard notes permissible manufacturer options for certain minimum lengths.
• Marking requirements:
  • Die nuts conforming to Table 1 must be marked with the thread designation as specified in ISO 2568.
  • Die nuts conforming to Table 2 (series R) must be marked with the letter R immediately followed by the thread designation (example shown: "R 1/8").
  • When tools fully conform to ISO, the ISO symbol may be added to the marking at the manufacturer’s discretion.
• References and related profiles: The standard references ISO thread and pipe standards (ISO 68, ISO 261, ISO 2568, ISO 7-1, ISO 228-1, etc.) for thread profiles and designations.

Applications

• Tool manufacturers: Designing and producing hexagonal die nuts to standardized dimensions for interchangeability.
• Fastener and tooling suppliers: Labelling and cataloguing dies that match customer thread specifications (metric, UNC/UNF, pipe threads, BSW/BSF/BA).
• Maintenance, repair and workshop technicians: Selecting correct hexagonal die nuts for on-site hand threading and thread repair.
• Quality and conformity assessment: Inspecting die nuts for compliance with standardized dimensions and marking for traceability.

Related standards

• ISO 2568 - Thread die designations and labelling
• ISO 68, ISO 261 - Thread profiles and series (metric)
• ISO 7-1, ISO 228-1 - Pipe thread designations and tolerances
• ISO 263, ISO 2563, ISO 4230/4231 - Complementary standards on thread cutting tools

Keywords: ISO 7226, hexagonal die nuts, hexagonal dies, thread dies, ISO metric threads, UNC, UNF, pipe threads series R, BSW, BSF, BA, marking, dimensions, tolerances.