Overview
ISO 7661:1984 - Aerospace - Fluid systems - Clamp blocks for tube lines having axial alignment - Design standard and qualification testing (Metric series) defines design, dimensions and qualification tests for clamp blocks used to fasten tubing in aerospace fluid systems. It covers clamp blocks with or without electrical grounding, for tube outside diameters selected from ISO 2964 (metric series, nominal range 4–32 mm), and specifies classification, dimensional limits and test methods for mechanical, electrical, climatic and flame-resistance qualification.
Key topics and technical requirements
- Scope & classification
- Clamp blocks are classified into Class A, B and C by tube diameter ranges and maximum heights (examples from the standard: Class A H = 27 mm, Class B H = 35 mm, Class C H = 48.5 mm).
- Supports axial alignment (tube axes in same plane) and include monobloc and modular designs with removable parts and optional inserts.
- Dimensional data
- Maximum heights, nominal radii and removable-part widths are tabulated per tube outside diameter (metric sizes).
- Modular bolt spacing equals the sum of removable-part and insert widths plus 10 mm; monobloc spacing equals the corresponding modular spacing.
- Temperature classes
- Designed per temperature classes in ISO 6771 (standard includes a Type III case up to +200 °C). Specific service ranges are referenced to ISO 6771.
- Electrical requirements
- For grounded clamp blocks, electrical contact resistance is measured before and after mechanical and climatic tests; acceptance ≤ 150 mΩ.
- Mechanical qualification
- Sliding tests (e.g., 6 mm displacement at 1 Hz, typical test temperatures +55 °C, +110 °C, +160 °C), contamination/fluids exposure (fuel, hydraulic fluids, de-icing, cleaning fluids, fire-extinguishing liquids), vibration and wear checks.
- Initial sliding force targets (example): 15–30 N depending on tube/material; post-test minimum sliding force > 5 N.
- Wear limits are defined (examples: maximum local wear allowances and percentage of tube thickness limits for light alloys vs stainless/titanium).
- Fastening screw tightening torque cited as 2 N·m for sliding tests.
- Climatic & corrosion tests
- Low/high temperature, salt spray and other climatic procedures are specified in accordance with ISO 7137.
- Flame resistance
- Small-scale flame test using Bunsen burner (flame temperature ~843 °C, 12 s exposure) with acceptance criteria for continued burning, flaming drops and ignition of a cotton indicator.
Applications and users
ISO 7661 is intended for:
- Aerospace designers and engineers specifying tubing supports in hydraulic, fuel and pneumatic systems.
- Manufacturers of clamp blocks and tube supports who need standardized dimensions and qualification protocols.
- Procurement and maintenance teams requiring verified, qualified clamp hardware for aircraft and spacecraft fluid systems.
- Test laboratories performing mechanical, electrical, climatic and flame-resistance qualification on aerospace components.
Related standards
- ISO 2964 - Aircraft tubing outside diameters and thicknesses (metric)
- ISO 5855 - Aerospace construction - MJ threads
- ISO 6771 - Pressure and temperature classifications for fluid systems/components
- ISO 7137 - Environmental conditions and test procedures for airborne equipment
- ISO/TR 2695 - Resistance to fire in designated fire zones
Keywords: ISO 7661, clamp blocks, aerospace fluid systems, tube lines axial alignment, qualification testing, metric series, tube diameters 4–32 mm, electrical grounding, sliding test, flame resistance.