Rod End Bearings and Spherical Bearings

Technical Terms & Definitions

Radial Static Load Capacity: The amount of load a bearing can support, in tension, or pull, before it breaks. If a part has a RSLC of 5,000 pounds, loading to this value could cause permanent damage. Operating loads should include a factor of safety, generally 4 to 1, but in any event should not be near the RSLC. Noting the capacity is a good comparator when making interchanges or up grading. See page 4 of catalog, or page 2 of “The ABC’S OF SPHERICAL ROD ENDS” for more information regarding loads.

Axial Static Load Capacity: The amount of load a bearing can support in the axial direction, through the ball bore, before permanent damage can occur. See page 4 of the Aurora Bearing Catalog for recommended Axial Static Load Capacities. Operating loads should include a factor of safety, generally 4 to 1, but in any event should not be near the ASLC.

Male Rod End: Externally threaded rod end.

Female Rod End: Internally threaded rod end.

Spherical Bearing: Consists of a raceway around a ball. To function, is placed in a housing, as it has no threaded portion to affix it to a component. Also sometimes called a mono-ball.

Metal on metal bearing: The wear surfaces of both the ball and race on a standard rod end or spherical bearing are a “metal” surface rubbing “on” a “metal” surface. A metal on metal bearing requires some sort of lubrication if regularly misaligned.

Ball: The spherical inner portion of the bearing, with a through hole for attachment. Also sometimes referred to as an “inner ring”.

Eared Ball: A ball with integral spacers on each side of the ball intended for high misalignment.

Race: The portion of the bearing that the ball rotates within. It can be machined into the body on a 2-piece rod end or be one solid ring on a 3-piece part. On a spherical bearing, the race is sometimes referred to as an “outer ring”

Teflon Liner: Teflon is a trademark held by Dupont for their material chemically known as PTFE. A teflon liner is a strip of PTFE/fabric composite bonded to the raceway of the part. It provides a self-lubricating surface for the ball to ride on. It should not be confused with virgin PTFE, which has very low compressive strength. A proper liner relies on the fabric component for load bearing capacity, and the PTFE component for lubricity.

“Zerk” fitting: Connection allowing passage of grease into bearing for lubrication. Sometimes known as a grease nipple, greaser, or zert fitting.

“Flush” fitting: Connection allowing passage of grease into bearing for lubrication. Unlike “zerk” fitting, fitting protrudes a minimal amount from surface, and requires a needle mating fitting to introduce lubricant.

Lubrication: A metal on metal bearing, when regularly misaligned or oscillated in operation, will require lubrication. A lightly loaded bearing may be run with minimal lubrication, relying on a boundary, or very thin, lubricant film. More heavily loaded, or frequently misaligned bearings require a film of lubricant between the ball and race, to prevent galling, or micro welding of the two surfaces. A sign of insufficient lubrication on a used metal on metal bearing is noticeable discoloration of the ball, either to black or brown, on the wear surfaces.
Imperial Thread: Also known as “inch thread”. Inch threads are identified by the nominal diameter size followed by the number of threads per inch. “5/16-24” indicates 5/16 inch outside diameter and 24 threads per inch.

Metric Thread: Metric screw threads are identified by the letter (M) for the thread form profile, followed by the nominal diameter size and the pitch expressed in millimeters, separated by the sign (x) and followed by the tolerance class separated by a dash (-) from the pitch. (ex.: M10 x 1.5-6g)

Bore: The diameter of the hole through the ball of a spherical bearing or rod end.

Shank: The threaded portion of a rod end. Will be either male, external thread, or female, internal thread.

Base to Center: The dimension that specifies the distance from the bottom of the shank to the center of the ball bore. This is the most common measurement in the bearing industry when the length/height of a rod end is expressed.

Staking Groove: Also known as the Grumman groove. A groove that is machined into a bearing or housing and is used to retain the spherical bearing in the housing.

Magnetic Particle Inspection: A method used to detect cracks, laps, seams, inclusions, and other discontinuities on or near the surface of the bearings.

Radial Clearance: In an unmounted bearing radial clearance is the amount of internal movement that the ball can travel along the axis perpendicular to the ball bore.

Axial Clearance: In an unmounted bearing axial clearance is the amount of internal movement that a ball can travel along the axis of the ball bore.

Swage: The cold forming of a race or body around a ball.

Stake: The retention of a ball or insert (bearing) in a housing.

Misalignment: The degree of angular movement that a ball can accommodate without interference.