Aircraft control linkages demand retention against vibration, controlled fatigue life, and documented traceability. The hardware stack around a rod end in aircraft service reflects those requirements directly.
AN bolts (clevis bolts). Aircraft rod end installations typically use AN bolts. These bolts have a close-tolerance shank, a drilled end, and an unthreaded grip section that fits the bore. The grip length matches the assembly width so the threads never sit inside the bore. Shear loads act on the smooth shank, not the thread root. Using a standard bolt with threads in the shear zone is an installation error that reduces fatigue life substantially.
Bushings. A hardened bushing is pressed or slipped into the rod end bore to protect the eye from the bolt bearing surface. Without it, the softer bore material fretts against the bolt under oscillating load, and the bore enlarges over time. Bushings take the wear and are replaceable. In corrosive environments, use stainless steel or bronze bushings with stainless steel rod ends. Carbon steel bushings can corrode and eventually bind in the bore.
Castle nuts and cotter pins. The castle nut is installed on the bolt, torqued to the specified value, and then aligned so one of its slots lines up with the cotter pin hole in the bolt shank. A cotter pin is inserted and bent against the bolt, preventing the nut from loosening under vibration. This is the positive locking method used in flight control linkages where a backed-off nut causes loss of control. The cotter pin must not be reused. It is a one-time part.
Large-area washers (safety washers). Placed against the rod end housing face, these washers' primary purpose is containment: if the ball and inner ring separate from the housing under fatigue or overload, the washer keeps the assembly from pulling through the open side and disconnecting the linkage. Clamp-load distribution is a secondary, incidental effect of any washer fitted under a nut. The washer OD should be at least equal to the housing OD so a separated ball cannot pass through.
Industrial designers apply the same stack for similar reasons: vibration, safety criticality, and the need for inspectable retention. The AN system is overdeveloped for most industrial uses, but the underlying logic (tight tolerances, positive locking, wear protection at the bore) is transferable to any high-reliability rod end installation.