ISO 6149-2:2006

Overview

ISO 6149-2:2006 - Connections for hydraulic fluid power and general use - Part 2 defines the dimensions, design, test methods and requirements for heavy‑duty (S series) metric stud ends with O‑ring sealing. It covers both adjustable and non‑adjustable stud ends with ISO 261 metric threads and specifies performance limits, identification, O‑ring details and required testing for hydraulic and general‑pressure applications.

Key topics and technical requirements

• Threading and dimensions: Stud ends use ISO 261 general‑purpose metric threads (tolerance grade 6g per ISO 965‑1). Detailed dimensional drawings and tables for S‑series stud ends are provided (see Figures 1–3 and Table 1 in the standard).
• Working pressures: Permissible working pressures depend on size, material and design. Typical limits given:
  • Non‑adjustable stud ends: up to 63 MPa (630 bar)
  • Adjustable stud ends: up to 40 MPa (400 bar)
  • Actual allowable pressure varies by thread size and application (see Table 2).
• Performance testing: Burst and cyclic endurance (impulse) tests are required and shall be conducted in accordance with ISO 19879. Conformance to dimensions alone does not guarantee rated performance - manufacturers must perform the specified tests.
• O‑rings: Default material for petroleum‑based hydraulic fluids is NBR (nitrile) with hardness 90 ± 5 IRHD and quality grade N per ISO 3601‑3. O‑ring sizes and tolerances are specified for S‑series stud ends.
• Design and assembly: Requirements for adjustable stud end washers (clinch washer fit, flatness allowances and maximum nut torques) are given (Table 3). Hex across‑flat tolerances follow ISO 4759‑1, product grade C.
• Identification & designation: Standardized marking and designation format (e.g., “Stud end ISO 6149‑2 – M18 × 1,5”) and machining/notch identification rules are specified.

Applications and who uses it

ISO 6149‑2 is intended for:

• Hydraulic system designers and OEMs specifying ports and stud ends for high‑pressure fluid power systems
• Component manufacturers (connectors, hose fittings, plugs) producing heavy‑duty (S series) stud ends
• Quality, testing and certification labs performing burst and impulse tests
• Maintenance engineers and procurement professionals ensuring interchangeability and safety in hydraulic installations

Practical uses include connections to tubes, pipes, hose fittings and cartridge valve plugs in industrial, mobile and offshore hydraulic equipment.

Related standards

• ISO 6149 series (Parts 1, 2, 3, 4) - recommended metric thread/O‑ring system for new hydraulic designs
• ISO 261 / ISO 965‑1 - metric thread definitions and tolerances
• ISO 3601‑3 - O‑ring quality acceptance criteria
• ISO 19879 - test methods for hydraulic fluid power connections
• ISO 8434‑1, ISO 8434‑3, ISO 8434‑4 - connector details referenced by ISO 6149‑2

Keywords: ISO 6149-2, stud ends, heavy‑duty S series, O‑ring sealing, ISO 261 metric threads, hydraulic fluid power, burst test, impulse test, NBR O‑ring.