Overview
ISO 299:1987 - "Machine tool tables - T-slots and corresponding bolts" standardizes the metric geometry and spacing of T-slots used on machine-tool tables and specifies the corresponding metric bolt sizes. This second edition (1987) cancels ISO 299:1973, removes inch-based dimensions, and adds additional requirements for slot designation and spacing. The standard enables interchangeability of clamping and fixturing components across machines built to the metric specification.
Key topics
- Slot dimensions in millimetres: Nominal T-slot widths (dimension A) and related geometric parameters (depth, radii/chamfers) are given in tables to ensure consistent manufacture and fit.
- Corresponding bolt sizes: Metric bolt thread sizes for use in the T-slots are specified and T-slots/bolts are designated by the bolt nominal thread (for example, M10).
- Slot tolerances: Different tolerance grades are specified for slot types - H8 for reference slots and H12 for clamping slots - to support accurate locating versus clamping functions.
- Pitch (spacing) options and tolerances: For each slot width there are three or four recommended pitch (P) values. Pitch tolerance bands are specified by ranges (e.g., smaller pitches have tighter allowances, larger pitches permit greater tolerance) and the tolerance on pitch is not cumulative.
- Design and layout guidance: Recommendations include choosing the most suitable pitch for a given table size, arranging slots symmetrically when possible, and identifying a reference slot (especially important when an even number of slots is used).
- Scope notes: The 1987 edition removed inch values; bolt sizes below 6 mm and above 36 mm were noted for future addenda where corresponding values did not exist in this edition.
Applications
ISO 299 is directly applicable to:
- Machine-tool table and workholding designers (ensuring compatibility of T-slots and fasteners)
- Machine manufacturers and OEMs (standardized production and interchangeability)
- Fixture and clamping hardware suppliers (bolt and accessory design)
- Maintenance, retrofit and tooling groups (replacement parts, fixture planning)
- CAD library authors and procurement teams (standard part selection and specification)
Using ISO 299 reduces tooling incompatibility, simplifies procurement of T-slot bolts and clamps, and improves cross-manufacturer interchangeability.
Related standards
ISO 299 should be used alongside general ISO metric fastener and thread standards and other machine-tool standards governing table construction and dimensional tolerances to ensure full compatibility across components and systems.
