ISO 7661:2024

Overview

ISO 7661:2024 - "Aerospace fluid systems - Clamp blocks for tube lines having axial alignment - Design requirements and qualification testing (metric series)" specifies dimensional requirements and qualification test methods for clamp blocks used to support axially aligned tubing on aerospace vehicles. The standard covers clamp blocks for tube outside diameters from 4 mm to 36 mm (selected from ISO 2964), and applies to both modular and monobloc clamp-block designs, with or without electrical grounding.

Key topics and technical requirements

• Scope and classification
  • Supports tube ODs 4–36 mm; clamp blocks are classified into Class A, B, and C based on OD ranges and maximum heights.
  • Two main designs: monobloc (two monobloc parts) and modular (removable parts and optional inserts).
• Dimensions
  • Standardized nominal radii, maximum heights per class, removable part widths (two models providing 3 mm or 5 mm clearance), and bolt spacing rules (modular spacing = sum of removable parts and inserts + 10 mm).
• Temperature service classes
  • Design for Type I (−55 °C to +70 °C), Type II (−55 °C to +135 °C) and Type III (−55 °C to +200 °C) environments in accordance with ISO 6771.
• Qualification tests
  • Electrical tests (for grounded blocks): measure contact resistance before and after mechanical/climatic tests using 1–4 A DC. Contact resistance ≤ 150 mΩ is required.
  • Mechanical tests: sliding test under temperature (3 samples, specified tube sizes, ±3 mm displacement at 1 Hz, 50 000 cycles at defined temperatures), sliding-force initial range (15–30 N), final requirement (> 5 N), and wear limits (aluminium 40 μm; stainless steel and titanium 15 μm). Vibration tests and other mechanical assessments are specified.
  • Climatic and flame-resistance tests: procedures include low/high temperature cycles, salt spray and flame-resistance apparatus and acceptance criteria (see clauses 7.3–7.4).
• Test documentation
  • Measurement procedures (e.g., electrical contact resistance, sliding force, wear measurements) are explicitly defined for qualification.

Practical applications

• Use ISO 7661:2024 when designing, specifying, procuring, qualifying or approving clamp blocks for aerospace fluid systems:
  • Aircraft and spacecraft integrators specifying tube supports
  • Component manufacturers producing monobloc or modular clamp blocks
  • Certification and quality teams performing qualification testing and acceptance
  • Maintenance and repair organizations assessing replacement components

Related standards

• ISO 2964 (tube outside diameters selection)
• ISO 6771 (pressure and temperature classifications)
• ISO 7137 (environmental conditions and test procedures for airborne equipment)
• ISO 2685 (flight test procedures referenced for flame/resistance context)

Using ISO 7661:2024 ensures consistent clamp-block geometry, reliable mechanical and electrical performance, and repeatable qualification testing across aerospace fluid-system applications.