MC757-255 – Caillau (SERFLEX) Worm Drive Hose Clamp (50-65mm)
Available now on the Airparts.aero Marketplace.
Overview
The MC757-255 is a high-quality, worm drive hose clamp manufactured by Caillau (under the SERFLEX brand). While sometimes specified under OEM part numbers (e.g., by Textron Aviation) or distributed by reputable suppliers like McFarlane Aviation, this clamp originates from Caillau's engineering standards. It is designed to provide a reliable, circumferential seal between a flexible hose and a rigid fitting or tube in various low-to-medium pressure aircraft applications. Note: This part number identifies a hose clamp, not an O-ring seal.
The clamp consists of a perforated or embossed stainless steel band, a stainless steel housing, and a worm screw (material varies by W3/W4 grade). Tightening the screw engages the band, causing it to constrict evenly around the hose. This mechanism provides a strong, consistent clamping force essential for maintaining the integrity of connections in fuel vent lines, coolant lines, environmental control system (ECS) ducts, and drain lines. Sourcing this clamp under its original specification or via trusted channels ensures it meets required material and performance standards.
Key Features
Industry Standard Design: A widely used worm drive clamp from Caillau (SERFLEX), recognized for its reliability in aerospace applications.
Worm Drive Mechanism: Provides high clamping force and a wide adjustment range for a secure, reliable seal.
Stainless Steel Band & Housing: Offers excellent resistance to corrosion from fluids and environmental factors common in aircraft engine compartments and airframes.
Smooth Band Underside (Typically): Designed to prevent damage to the hose material during tightening and under vibration.
Consistent Clamping Force: The worm gear allows for precise torque application, resulting in predictable and uniform pressure around the hose circumference.
Technical Specifications
Part Number: MC757-255
Component Type: Worm Drive Hose Clamp
OEM Manufacturer: Caillau (SERFLEX)
Material (Band & Housing): Stainless Steel (Typically AISI 430 or 304 - W3/W4 grade). Specific grade confirmation depends on source/certification.
Material (Screw): Zinc-Plated Steel (W3) or Stainless Steel (W4). Specific grade confirmation depends on source/certification.
Finish: Natural Stainless Steel (Band/Housing), Zinc Plate (Screw, if W3).
Clamping Diameter Range: 50 mm to 65 mm (approx. 1.97 inches to 2.56 inches)
Band Width (Typical): 9 mm or 12 mm. Confirmation depends on source/certification.
Governing Standard (Typical): Conforms to DIN 3017 principles. OEM specifications may apply if sourced via OEM part number.
Aircraft Compatibility
The MC757-255 clamp is used on a wide variety of aircraft where a high-quality worm drive clamp within this size range is required for low-to-medium pressure applications.
Representative Platforms:
Cessna Piston Aircraft
Beechcraft Piston Aircraft
Cessna Caravan Series
Piper Aircraft
Business Jets (in non-primary systems)
Experimental Aircraft
Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility for a specific hose connection.
Applications
Securing flexible ducting in Environmental Control Systems (ECS) and ventilation systems.
Clamping coolant hoses on liquid-cooled engines.
Securing drain lines and vent hoses.
Attaching low-pressure oil lines (e.g., breather lines).
WARNING: Not typically suitable for high-pressure hydraulic lines or fuel lines requiring fire resistance, which usually mandate specialized cushioned loop clamps (e.g., MS21919) or specific fittings.
Why Choose MC757-255?
While seemingly a simple component, the reliability of hose clamps is critical for preventing leaks of flammable fluids, loss of cabin pressure, or ingress of contaminants. A certified clamp like the MC757-255 guarantees the use of the correct grade of stainless steel to prevent corrosion failure and ensures the worm drive mechanism is manufactured to tolerances that prevent stripping or slipping under proper torque. Using a non-certified, automotive-grade clamp introduces risks associated with material incompatibility, corrosion susceptibility, and potential failure under vibration.
The MC757-255 worm drive hose clamp operates on the fundamental mechanical principle of a screw thread converting rotational motion into linear motion and high clamping force. The worm screw acts as an inclined plane wrapped around a cylinder. As the screw is turned, its threads engage the slots or embossments in the flexible band. Each rotation of the screw pulls a specific length of the band through the housing, incrementally decreasing the clamp's diameter. Because the pitch of the screw thread is very fine, a small input torque applied to the screw head generates a significantly amplified tensile force in the band, according to the principle of mechanical advantage ($MA = 2\pi r / p$, where r is the lever arm radius and p is the thread pitch). This high tensile force translates into a uniform radial compressive pressure exerted by the band onto the hose, creating a secure seal against the underlying fitting. The design is inherently non-backdriving, meaning vibration is unlikely to cause the screw to loosen.
Note: This is a common but potentially flight-critical hardware component depending on the system it secures. Installation must be performed by a certified mechanic. The clamp must be the correct size for the hose and fitting combination. It should be tightened using a calibrated torque tool to the value specified in the aircraft maintenance manual. Over-tightening can damage the hose or the clamp mechanism, while under-tightening will result in leaks. Inspect clamps regularly for security and signs of corrosion.
Documentation
Technical details are based on the standard Caillau (SERFLEX) MC757 product line. Specific OEM requirements must be referenced in the applicable aircraft maintenance manuals and IPCs if sourced via an OEM part number.
Caillau / SERFLEX Product Information (Reference): Available on the manufacturer's website.
McFarlane Aviation Catalog (Reference): May list this part as a distributor.