Load Ratings & Misalignment Capabilities
Definitions for Rod End and Spherical Bearing Terminology
Radial Load  Axial Load  Static Load  Dynamic Load  Static Radial Limit Load  Static Radial Ultimate Load
Static Axial Limit Load  Static Axial Ultimate Load  Axial Proof Load  Rotation  Misalignment
Oscillating Radial Load or Dynamic Load  Radial Play  Axial Play  Fatigue Load of Rod Ends
Load Ratings: Spherical Bearing  Rod End Bearing  PV Factor  Dynamic Oscillating Radial Load
NHBB Testing Capabilities: Mechanical  Polymer  Specifying Misalignment
Radial Load
A load applied normal to the bearing bore axis (A).
Axial Load
A load applied along the bearing bore axis (B).
Radial/Axial Load
Static Load
The load to be supported while the bearing is stationary.
Dynamic Load
The load to be supported while the bearing is moving.
Dynamic Load
Static Radial Limit Load
The static load required to produce a specified permanent set in the bearing. It will vary for a given size as a function of configuration. It may also be pin limited, or may be limited as a function of body restraints as in the case of a rod end bearing. Structurally, it is the maximum load which the bearing can see once in its application without impairing its performance.
Static Radial Ultimate Load
The load which can be applied to a bearing without fracturing the ball, race or rod end eye. The ultimate load rating is usually, but not always, 1.5 times the limit load. Plastic deformation may occur.
Static Axial Limit Load
The load which can be applied to a bearing to produce a specified permanent set in the bearing structure. Structurally, it is the maximum load which the bearing can see once in its application without impairing its performance.
Static Axial Ultimate Load
The load which can be applied to a bearing without separating the ball from the race. The ultimate load rating is usually, but not always, 1.5 times the limit load.
Axial Proof Load
The axial load which can be applied to a mounted spherical bearing without impairing the integrity of the bearing mounting or bearing performance. It is always less than the static axial limit load. Bearing movement after proof load is usually .003 or less.
Rotation
Is the relative angular displacement between the ball and race that occurs within the plane perpendicular to the axis of the ball bore. The direction of rotation is about the axis of the ball bore.
Rotation
Misalignment
Is the relative angular displacement between the ball and race that occurs within any plane that coincides with the axis of the ball bore (see Radial/Axial above). The direction of misalignment is about any axis perpendicular to the ball bore.
Oscillating Radial Load or Dynamic Load
The unidirectional load produces a specified maximum amount of wear when the bearing is oscillated at a specified frequency and amplitude. This rating is usually applied to selflubricating bearings only. The dynamic capability of metaltometal bearings depends upon the degree and frequency of grease lubrication, and that of dry film lubricated bearings upon the characteristics of the specific dry film lubricant applied.
Radial Play
Radial play (or radial clearance) is the total movement between the ball and the race in both radial directions less shaft clearance (when applicable). Industry specifications have established the gaging load at ±5.5 lbs., and this is now considered as the industry standard. Unless otherwise specified, the industry wide standard for metaltometal spherical bearing and rod end radial clearance is “freerunning to .002 max.” Radial play is sometimes referred to as “Diametral clearance.” The two terms are synonymous.
Radial Test Fixture 
Method of Measuring Radial Play 
Axial Play
Axial play (or axial clearance) is the total movement between the ball and the race in both axial directions. The gaging load is again ±5.5 lbs. Axial play is a resultant, being a function of radial play, of ball diameter and race width. The ratio between radial and axial play varies with bearing geometry.
Axial Test Fixture
Fatigue Load of Rod Ends
Aerospace Standard series rod end bearings AS81935 must be capable of withstanding a minimum of 50,000 cycles of loading when tested as follows: The loading must be tensiontension with the maximum load equal to the fatigue loads listed on the NHBB drawing of the ADNE and ADN series rod end bearings. The minimum load must be equal to 10% of the fatigue loads.
Load Ratings
The load rating of a bearing is determined by the dimensions and strength of its weakest component. External factors, such as mounting components, pins, bolts, and housings are not considered part of a bearing when load ratings are investigated but should be considered separately.
Spherical Bearing Load Ratings
The weakest part, or loadlimiting area, of a spherical bearing is its race. For this reason, formulas have been developed that use the race to calculate static load ratings based on size and material strength. The static load rating formulas for selflubricating and metaltometal spherical bearings are shown below. These formulas will yield approximate ratings, which should be used as ballpark numbers for bearing design.The allowable radial stress values given in the tables were determined from the ultimate tensile strength specifications for various race materials. Allowable axial stress values were derived from material yield strengths.
Static Load Rating Formulas for Allowable Stress PTFE Lined Bearings (psi)

Static Load Rating Formulas for

Bearing Size Bore Code 
G Width 
3 & 4  .062 
510  .078 
1216  .094 
20 & above  .109 
Allowable Stress MetaltoMetal Bearings (psi)
Race Material  Radial 
Axial 

Ultimate 
Limit 
Ultimate 
Limit 

174PH, Rc3236  150000 
100000 
125000 
83000 
4130 Rc3236  150000 
100000 
125000 
83000 
A286 (AMS 5737)  140000 
93000 
95000 
63000 
AMPCO® 15 Bronze  75000 
50000 
45000 
30000 
AMPCO® is a registered trademark of AMPCO Metal Inc.
Rod End Bearing Load Rating
Rod end bearing load ratings can be generated only after carefully determining the load restrictions that each element of the rod end bearing imposes on the entire unit. In order to generate a frame of reference, consider the rod end bearing as a clock face, with the shank pointing down to the 6 o’clock position. The limiting factors in rating a rod end bearing are as follows:
 The double shear capability of the bolt passing through the ball bore.
 The bearing capability, a function of race material or selflubricating liner system.
 The rod end eye or hoop tension stress in the 3 o’clock9 o’clock position.
 The shank stress area, as a function of male or female rod end configuration.
 The stress in the transition area between the threaded shank transition diameter and the rod end eye or hoop.
Most rod ends will fail under tension loading in about the 4 o’clock8 o’clock portion of the eye or hoop. The Net Tension Area (NTA) can be found as follows:
This simple rod end load rating formula does not take into consideration such variables as special body shapes, thin race sections, hardness variation, lubrication holes, grooves, and hoop tension, which could significantly affect the load rating. Contact NHBB Applications Engineering for assistance in determining the load rating for specially designed Rod Ends and Sphericals.
The shank stress area (SSA) is a function of being either male or female, as follows:
The axial load capability of a rod end is a function of the following:
 The retention method used to mount the bearing in the rod end eye (see the Bearing Installation and Retention section).
 The axial load capability of the bearing element.
 The bending moment, if any, placed on the rod end.
PV Factor
While not a type of loading, the PV factor is very useful in comparing and predicting test results on high speedlow load applications such as helicopter conditions.
PV is the product of the stress (psi) and the velocity (fpm) applied to a bearing. Caution must be advised when considering extreme values of psi and fpm. The extreme must be considered individually, as well as together.
Because the PV factor is derived from the geometry and operating conditions of a bearing, it serves as a common denominator in comparing or predicting test results. For this reason PV values are included in the wear curves for liners in the SelfLubricating PTFE Liner Systems section.
The formula for determining the PV value for a spherical bearing is as follows:
Dynamic Oscillating Radial Load
The dynamic oscillating radial load ratings given in this catalog for ADB, ADW, ADBY, ADBN, ADWN, ADBL and ADWL series selflubricating spherical bearings are based on testing in accordance with AS81820. For conditions other than those specified by AS81820 contact NHBB Applications Engineering.
NHBB Testing Capabilities
Mechanical Test Equipment
NHBB has a variety of equipment to test spherical and rod end bearings under diverse conditions. NHBB performance data exceeds military and individual manufacturers’ design requirements. Maximum capabilities of NHBB testing machines are shown below.
NHBB Testing Capabilities  
Force 

Material Testing (Universal Testing Machine)  110,000 Lbs. 
Static Compression/Tension  200,000 Lbs. 
Low Speed Oscillation (up to 50 cpm) Unidirectional Loading (1 machine, 2 station) (700°F) (1 machine, 2 station) (700°F) 
20,000 Lbs. 70,000 Lbs. 
Moderate To High Speed Oscillation Unidirectional Load (room temp.) (1 machine, 2 station) (1000 cpm) (1 machine, 2 station) (1500 cpm) (1 machine, 6 station) (200600 cpm) 
1,000 Lbs. 1,000 Lbs. 8,000 Lbs. 
Low Speed Oscillation Reversing or Alternating Load (room temp.) (1 machine, 2 station) (up to 50 cpm) 
40,000 Lbs. 
High Speed, Oscillation Reversing and Alternating Load (room temp.) (2 machines, 1 station each) (400 cpm) 
2,500 Lbs. 
Airframe Track Roller Testing Machine (roller against flat plate) 
60,000 Lbs. 
Polymer Test Equipment
NHBB has the following thermal analysis (TA) equipment to support and control the quality of composites/polymers through analytical techniques that measure the physical and mechanical properties as a function of temperature and time:
 Differential Scanning Calorimeter (DSC)
 Thermogravimetric Analyzer (TGA)
 Dynamic Mechanical Analyzer (DMA)
 Thermomechanical Analyzer (TMA)
 ThermoOxidative Stability Test (TOS)
 Acid Digestion System
 Fourier Transform Infrared Spectroscopy (FTIR)
Formula for Determining Misalignment of Rod End & Spherical Bearings
Most standard rod end and spherical bearing misalignment angles specified in NHBB catalogs are based on this method. 
This method may be used as design reference for installation purposes, but should not be used as a functioning misalignment under load. 
(Neck balls only) 
How NHBB Specifies Catalog Bearing and Rod End Misalignment
The misalignment angle of a rod end or spherical bearing refers to the angle between the ball centerline and the outer member centerline when the ball is misaligned to the extreme position allowed by the clevis or shaft design, as applicable.
NOTE: Since angle “A” applies equally on both sides of the centerline, it follows that total misalignment of the bearing is double the value obtained for “A”.
The illustrations show varying types of bearing misalignment and a formula for calculating each where:
A = angle of misalignment 
B = bore of ball 
The misalignment angle illustration below shows how misalignment angles for standard ball spherical bearings and rod ends are represented in NHBB catalogs. The misalignment angle is calculated per the Standard Method. Neck ball (high misalignment) bearings and rod ends are represented in the same manner, but are calculated per the High Misalignment Series Method.
NHBB prefers not to use rod end clevis misalignment for the following reason. The rod end clevis misalignment formula presupposes a clevis configuration as shown in which the clevis slot and ball faces are of equal width and in direct contact. In aircraft applications the configuration shown is more typical than that shown in the Rod End Clevis Misalignment illustration . As pictured in the Typical installation, the clevis slot is wider than the ball to permit installation of flanged bushings and/or spacers. This results in a higher but more variable misalignment capability, and the angle of misalignment becomes a function of the user’s bushing flange or spacer diameter instead of the fixed rod end head diameter.
Misalignment Angle 
