MS28782-6 - Military Standard Retainer Ring

MS28782-6 – Military Standard Spiral Retaining Ring (0.375" Bore)

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Overview

The MS28782-6 is a high-strength, military standard spiral wound retaining ring engineered for the precise axial positioning and retention of components within a 0.375-inch (3/8") diameter bore or housing. This is not a conventional snap ring; it is an advanced fastening component coiled from flattened carbon spring steel wire, designed to provide a uniform, 360-degree retaining shoulder. Its primary function is to securely locate bearings, seals, gears, and other critical parts within housings, actuators, and various aerospace mechanical assemblies.

Manufactured in strict accordance with MS28782 (now NASM28782), this multi-turn ring is installed by winding it into a simple rectangular groove machined within the housing bore. Unlike a stamped snap ring with lug ears and gaps, the spiral ring exerts a uniform radial force and provides continuous contact with the groove, enhancing its load-bearing capacity and fatigue resistance. The phosphate coating provides corrosion protection suitable for many internal aerospace applications.

Key Features

• Military Specification Compliance: Manufactured and tested in strict accordance with MS28782 / NASM28782, guaranteeing material properties, dimensional accuracy, and performance.

• Spiral Wound, Multi-Turn Design: Typically features two turns, providing a continuous, gapless 360-degree retaining shoulder for uniform load distribution and superior strength compared to snap rings.

• High-Strength Carbon Spring Steel: Fabricated from certified carbon spring steel (per SAE 1070-1090), heat-treated to achieve high tensile strength and the necessary elasticity to securely grip the groove.

• Designed for Internal Grooves (Bores): Specifically engineered to be installed within a housing or bore to retain components axially.

• Phosphate Coated Finish: Provides corrosion resistance per MIL-DTL-16232, Type Z, Class 2, suitable for general aerospace internal environments.

• Lightweight and Low Profile: Offers high retaining strength within a minimal radial and axial space envelope, contributing to weight and space savings.

• No Lugs or Ears: The gapless design eliminates protruding features that can interfere with adjacent components.

Technical Specifications

• Part Number: MS28782-6

• Component Type: Spiral Wound Retaining Ring (Internal)

• Governing Specification: MS28782 / NASM28782

• Material: Carbon Spring Steel (per SAE 1070-1090)

• Finish: Phosphate Coat per MIL-DTL-16232, Type Z, Class 2

• For Housing Bore Diameter: 0.375 inches

• Groove Diameter (Ref): 0.406 inches

• Ring Free Outside Diameter (Approx): 0.420 inches

• Wire Cross-Section: Per MS28782 standard.

Aircraft Compatibility

The MS28782-6 is a standard hardware component used across all sectors of the aerospace industry where a high-reliability retaining ring for a 0.375" bore is required. It is not specific to a single aircraft but is a staple in the design of:

• Military Aircraft

• Commercial and Transport Category Aircraft (Boeing, Airbus)

• Business and Corporate Jets (Textron Aviation, Bombardier, Gulfstream)

• General Aviation Aircraft and Rotorcraft

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft or component Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility.

Applications

• Axial retention of bearings within gearbox housings, wheel hubs, and accessory drives.

• Securing seals, glands, and pistons within hydraulic and pneumatic actuators and accumulators.

• Positioning gears, sprockets, and pulleys on shafts within housings.

• Any mechanical assembly requiring a secure, low-profile internal retaining ring for a 3/8" bore.

Why Choose MS28782-6?

The failure of a retaining ring in a critical application can lead to the catastrophic disassembly of a component. The MS28782-6 spiral retaining ring offers superior performance compared to basic snap rings due to its gapless design, which provides uniform contact and prevents stress concentrations in the groove. Using a certified MS-spec part guarantees the correct material, heat treatment, and dimensional tolerances required to ensure the ring provides its full rated thrust load capacity and remains securely seated under all operational stresses.

The engineering advantage of the MS28782-6 spiral retaining ring lies in its superior stress distribution compared to a traditional snap ring (circlip). A snap ring makes contact with its groove at only three points (near the lugs and opposite the gap), concentrating the retained load and potentially leading to groove deformation or ring failure under high thrust or impact loads. The multi-turn spiral design of the MS28782-6 provides a continuous 360-degree contact surface against the groove wall. This distributes the axial thrust load uniformly around the entire circumference. This uniform loading significantly reduces the peak stress within both the ring and the groove material, allowing the spiral ring to often handle higher thrust loads than a snap ring of equivalent size and material, while also increasing the fatigue life of the groove itself. Furthermore, the installation process requires the ring to be slightly compressed radially, causing it to exert a continuous outward spring force against the bottom of the groove, ensuring it remains dynamically stable and securely seated even under heavy vibration.

Note: This is a flight-critical hardware component. Installation and removal typically require specialized tools or techniques to wind the ring into or out of its groove without overstressing or permanently deforming it. Re-use is generally permissible if the ring remains within its specified dimensional tolerances and shows no signs of damage or deformation. Always consult the component maintenance manual for specific instructions.

Documentation

The military standard governing this part is publicly available through the Department of Defense ASSIST database.

• ASSIST Document Summary Page for MS28782: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=45934