Ball Grade Terms, Glossary Terms

Whenever physical properties (size, geometry, etc.) are critical, the way terms are used becomes critical.  Even commonly used terms are often misinterpreted.  To make sure everyone gets exactly what they expect, we have developed standardized explanations for some of the most common ball terms.


 — Ball Grade Terms

Ball Diameter Variation: The difference between the largest and the smallest single diameter measurements of one ball.

Ball Grade: A specific combination of dimensional, form and surface roughness tolerances. A ball grade is designated by the grade number.

Basic Diameter: The size ordered which is the basis to which the “Diameter Tolerance” specification applies.

Basic Diameter Tolerance: The maximum allowable deviation of any ball mean diameter from the Basic Diameter, in any shipment to fill orders for that Basic Diameter.

Container Marking Increment
: The standard unit steps, in millionths of an inch, used to express the Specific Diameter.

Deviation from Speherical Form: The greatest radial distance in any radial plane between a sphere circumscribed around the ball surface and any point on the ball surface.

Hardness: The measure of resistance to penetration of the ball surface or truncated flat of the ball by a specified indenting shape as determined by specified methods.

Lot: A definite quantity of balls manufactured under conditions which are presumed uniform and which is considered and identified as an entirety.

Lot Diameter Variation: The difference between the mean diameter of the largest ball and that of the smallest ball in the lot.

Nominal Ball Diameter: The diameter value which is used for the purpose of general identification of a ball size, e.g. 1/4″ 6mm, etc.

Passivation: A chemical treatment to remove corrodible surface impurities and to provide a protective film. This term is applicable to corrosion resisting balls only.

Specific Diameter: The diameter marked on the unit container, expressed in the grade’s standard marking increment nearest to the mean diameter of the balls in that container.

Surface Roughness: Surface roughness consists of all those irregularities which form surface relief and which are conventionally defined within the area where deviations of form and waviness are eliminated.

Waviness: The more widely spaced circumferential component of surface texture. (Lacking standarized practices in this field, the specifications and tolerances for waviness are subject to agreement between manufacturer and customer.)

 — Glossary Terms

AFBMA – Anti-Friction Bearing Manufacturers Association; An organization of bearing manufacturers with established standards for balls and bearings.

ANSI – American National Standards Institute; A private, non-profit organization that administer and coordinates the U.S. voluntary standardization and conformity assessment system.

Annealed – A metalgraphic process in which a ball is softened. An annealed ball can be ground, drilled, filed and welded. Heated to remove or prevent internal stress; free from internal stress by heating and gradually cooling; toughened or tempered.

Application – an act of putting to use.

Ball – A sphere; a round body of various sizes and materials, either hollow or solid.

Ball Diameter – A width of a sphere indicated by fractions of an inch. For example: _” _”, _”. When balls are ordered by this size designation, it is the basis on which the diameter tolerance per carton and diameter tolerance per shipment applies. This diameter indication is also known as the “nominal diameter.”

Brinell Scale – A system of numerical notation called Brinell that measures hardness of the specific ball material as compared to the Rockwell Scale.

Burnish – To polish by friction; to make smooth and bright, especially by rubbing or friction; to brighten or make lustrous.

Burnishing – A process in which non-precision balls are used as a media to smooth or brighten parts in tumbling barrels. Burnishing media is mostly made of carbon steel.

Case Depth -A distance from the surface of the ball to the unhardened core. It is measured radially from the surface to a point where carbon content or hardness becomes the same as the core.

Chemical Certification – A form that certifies the chemical analysis of the material.

Corrosion Properties – An element that is within the chemical analysis of a specific material that can resist against corrosion (example: stainless steel alloys).

Crushing Strength – A resistance of a ball to crushing loads. It is measured in pounds as determined by the three-ball method.

Density – Mass per unit volume is measured by pounds per cubic inch.

Diameter Tolerance per Shipment – A permissible range of diameters of individual balls within any one shipment. It applies to all shipments for that basic diameter and is sometimes called “basic diameter tolerance.”

Diameter Tolerance per unit Container – A permissible range of average diameters of individual balls within any one unit container.

Durometer – A term that is used to indicate the hardness of plastic or rubber. The higher the durometer, the harder the ball as compared to the same Shore A scale.

Eddy Current Tester – A machine to safeguard the quality in final inspection and to check for surface cracks.

EDM – Electric Discharge Machining is a process that utilizes an electrode to create a hole or threads in a hardened ball.

Ferrous – A metal ball that contains iron in the content of the chemical analysis, such as chrome steel.

Final Inspection – A quality process that assures the ball order is to the exact specification of size, material and tolerance needed.

Flashing – A process that gives a ball blank a rough finish and removes the excess material around the ball.

Forge – To form by heating and hammering; to beat into shape; to make by concentrated effort.

Grade – A guaranteed sphericity expressed in millionths of an inch. For example, a grade 25 ball is spherically accurate within 25 millionths of an inch.

Grinding – A process in which balls are polished or smoothed with a grinding wheel to make a ball a smaller size.

Heading – A process that produces slugs from raw wire or rod material through cold forging.

Heat Treating – A high temperature process that hardens the ball by subjecting a metal or alloy to controlled heating and cooling to improve hardness and other properties.

HFC -Headed, Flashed and Cleaned is when the ball is not put through any lapping process to make a precision tolerance. HFC balls are not hardened allowing them to be machined.

Hollow – A ball that has a space or empty cavity in the middle and is mostly used for decorative purposes or in floating applications.

ISO – International Standardization Organization – A group that sets policies and procedures for industry standards in the manufacturing of products.

Lapping – A process that polishes the ball to a shiny finish and to the exact size required.

Micrometer – A tool to measure the accuracy of the ball size; any of various devices for measuring minute distances; also called a mike, a precision instrument with a spindle moved by a finely threaded screw; for the measurement of thicknesses and short lengths, commonly used by machinists and inspectors.

MS Numbers– A Military Standard number is assigned by the Department of Defense to represent a certain size, material and tolerance of a ball.

Non-Ferrous– A metal ball that has no iron content in the chemical analysis, such as Brass, Aluminum, and Copper.

OEM – Original Equipment Manufacturer.

Oxidize – A process in which a ball can change color or develop a surface condition due to the influence of outside contaminants; to combine chemically with oxygen; to cover with a coating of oxide of rust.

Physical Certification – A form that certifies the physical properties of the material.

Polished – A process in which a ball is put into a lapping machine and tumbled to improve the finish.

Precision – The degree of refinement with which an operation is performed or measurement stated.

Quality control– A set of procedures determined by an organization that the quality of the ball is met with certain standards.

RMS – Root mean square; the square root of the arithmetic mean of the squares of the numbers in a given set of numbers determining the surface finish in micro inches.

Rockwell Hardness – A term that signifies the hardness of the ball, which is measured on various scales on a device, called a Rockwell tester.

Soft Polished – A ball that has not been heat-treated, for example a material that is already soft such as carbon.

Special Burnishing – A process in which a ball is put through tumbling barrels to make the balls completely round without flat spots.

Sphericity – Roundness which measures the difference between the largest diameter and the smallest diameter on a single ball.

Surface Waviness – A geometric irregularity of the ball surface. The wavelengths are longer than roughness.

TalyRand – An instrument that measures the roundness of the ball.

TalySurf – An instrument that checks the surface of the ball.

Tempering – A process that runs a ball for a specific length of time at a specific temperature to accomplish a specific Rockwell hardness; a substance added to modify other properties; the degree of harness and strength imparted to a metal, as by heat treatment.

Tensile Strength – Amount of pressure or psi the raw wire can withstand; the resistance of a material to longitudinal stress measured by the minimum amount of longitudinal stress required to rupture the material.

Tumbling – A process used to cut balls and smooth them. It also is used to make a ball shiny.

Tumbling Barrel – A drum in which objects are loosely placed and subjected to a tumbling action, as for mixing or polishing

Vacuum Melt – A process in which material is melted twice to make very fine steel.

Valve Grade – A process in which a ball is lapped twice for a fine finish.

Visual Inspection – Observation of the ball surface by the naked eye. It is also called macroscopic inspection.