Overview
ISO 2568:1988 specifies the general dimensions, interchangeability and marking of circular screwing (threading) dies and hand-operated die stocks. Applicable to both hand- and machine-operated circular screwing dies, the standard defines dimensional characteristics tied to thread diameter and pitch and covers a broad set of thread systems used in industry.
Key topics and technical requirements
- Scope of application
- Applies to ISO metric threads (coarse: M1 to M68; fine: M1 to M56).
- Applies to ISO inch threads of the Unified family (UNC and UNF): UNC from No. 1‑64 to 2 3/4 ‑ 4; UNF from No. 0‑80 to 1 1/2 ‑ 12.
- Annex B gives guidance (non‑normative) for non‑ISO inch threads: BSW, BSF, and BA types.
- Dimensional data
- Specifies general die dimensions as functions of thread diameter and pitch: outside diameter, thickness, cutting portion length, and attachment dimensions.
- Dimensional tables and cut‑length data are provided (Annex A and main tables).
- Die stocks - interchangeability
- Defines interchangeability dimensions for hand‑operated die stocks so dies from different manufacturers can fit standard holders (see Table 5 and Figure 3).
- Tolerance and classes
- Two classes of dies: precision and non‑precision.
- For precision dies tolerances are specified (example: on D = f10; on E = js12). For non‑precision dies tolerances on D and E are left to the manufacturer’s discretion.
- Marking
- Clause added in this edition requires dies to be marked with thread designation (examples: "M12 x 1.25", "1/4‑20‑UNC", "No. 12‑28‑UNF", "1/2‑12‑BSW").
- Manufacturers may append the ISO symbol when fully conformant.
Applications and users
- Manufacturers of threading dies and die stocks who need to design to recognized dimensions and ensure interchangeability.
- Toolmakers, maintenance workshops and metalworking shops choosing or replacing dies for manual or machine threading.
- Purchasing and quality teams specifying tooling to guarantee compatibility across suppliers.
- Technical authors and standards engineers documenting tooling specifications.
Practical benefits
- Ensures interchangeability of dies and die stocks across suppliers.
- Simplifies procurement by standardizing marking and dimensional references for metric and inch threads.
- Facilitates correct selection of precision vs. non‑precision dies based on tolerance requirements.
Related standards
- ISO 2568 references other ISO work (prepared by ISO/TC 29). For taper pipe threads see ISO 4230 (referenced in notes for R‑series threads).