Rod end bearings are used on the ends of cylinders, linkages, rods, and shafts to take up angular misalignment between connected parts. They consist of a spherically-shaped inner ring and a cylindrical bore for shaft mounting. Metallic rod end bearings are made of brass, bronze, iron, or steel and often plated with zinc or chromium. Non-metallic products are made of plastic, nylon, or Teflon®, a registered trademark of DuPont. Rod end bearings attach to rods and shafts via a male stud with external threads or a female housing with internal threads. Right-handed threads tighten in a clockwise direction and are the most commonly used type of thread. Left-handed threads tighten in a counterclockwise direction and must match the mating part. Load capacity and maximum angular misalignment are the most important specifications to consider. In most cases, bearing motion is symmetrical and the maximum angular misalignment is half of the total side-to-side range.
Specifications and Features
Rod end bearings differ in terms of dimensional specifications and special features. Dimensional specifications include design units, bore diameter, major diameter, bearing thickness, housing diameter, overall length, and thread length. English design units include inches (in) and fractions of an inch. Metric design units include millimeters (mm) and centimeters (cm). Bore diameter is the inner diameter (ID) of the bearing bore. Major diameter is the nominal diameter to the top of the threads. Bearing thickness is the length through the bore. Housing diameter is the outside diameter (OD) of the bearing housing. Overall length is the distance from the top of the housing to the end of the shank. In terms of special features, some rod end bearings are self-lubricating or include a lubrication port. Others are corrosion-resistant or equipped with Teflon seals.
Rod end bearings are used in applications that accommodate low to moderate shaft misalignment. They are also used in many aerospace, military, and automotive applications. Airframe control bearings are usually manufactured in accordance with U.S. military specifications (MIL-SPEC) such as MIL-B-7949 and MIL-B-6039. Rod end bearings with balanced designs are manufactured to meet NAS661, a standard specification for civilian aircraft. In the automotive industry, rod end bearings are used in steering knuckles and transmission linkages.
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Spherical Plain Bearings
Spherical plain bearings accommodate wide-ranging angular misalignment with a ball-and-socket type design. They are frequently used in linkages and control rod applications.