Why Use a Large OD Washer Beside a Rod End?

The failure mode it prevents. A rod end housing has a pressed-in or swaged-in inner ring and ball. Under fatigue loading, corrosion, or an overload event, the inner ring can separate from the housing. When that happens, the ball and inner ring are free to slide axially along the pin. Without a washer large enough to span the gap, the separated assembly pulls through the open side and the linkage loses all connection. This is a catastrophic failure in any control linkage.

How the washer prevents it. The washer OD must be larger than the housing eye bore. It must also be large enough to prevent the separated ball from passing through the gap between the bolt head and the washer face. The inner diameter clears the bolt shank. The washer sits against the housing face and captures any separated internal component. The linkage remains physically connected even after bearing separation.

When is it required? In aircraft, it is required on any rod end that is not positively retained by surrounding structure on the open side. If the housing eye is fully enclosed by both bracket walls, no separate washer is needed. The bracket itself provides the containment. A rod end installed in single shear with one open face always needs a washer on the open face.

In motorsport, most sanctioning bodies mandate safety retaining washers for the same reason. In industrial and marine applications, a retaining washer may not be mandatory, but the same engineering rationale still applies. For safety-critical linkages such as steering, lifting, braking, and flight-control systems, include a retaining washer.

Sizing guidance. The washer OD should equal or exceed the OD of the rod end housing. The washer must be beveled or chamfered at the inner edge to allow the rod end full angular travel without the housing contacting the washer face. A flat washer with a small ID restricts articulation. The bevel must be machined to match the maximum angular range of the specific rod end.