Balls have been used for decades for a wide variety of applications.  Especially the use of steel balls, stainless steel balls and carbon steel balls has been indispensable since the beginning of industrial production. To ensure the comparability, uniformity and quality of steel balls, they are manufactured according to the DIN 5401 standard, which provides information on grades, degrees, hardness and materials.


In the beginning was the wire. This is cut into small pieces. This is the start of the production of a metal ball. The cylindrical wire pieces are heated, compressed with the help of a ball press and thus already obtain a spherical shape. These still misshapen steel balls are rolled between two metal discs until they have acquired a nice spherical shape. To make the metal balls wear-resistant, they are then hardened. After hardening, the balls are ground until they reach the desired diameter and grade. In a final manufacturing step, the steel balls are polished. After the diameter, surface finish and shape have been checked one more time, the manufacturing process is complete.


When ordering steel balls, the dimensions of the desired ball are crucial. The decisive dimension is the diameter, which is specified in mm or inches. The surface finish is expressed in degrees, the smaller the degree, the higher the quality of the precision ball. The accuracy of the precision ball is 1µ. Another criterion in choosing the right steel ball is the right material from which the steel ball is made. Almost all types of steel can be used as the material, but rolling bearing steel and stainless steel are the most common. The use of stainless steel balls offers good corrosion resistance, for example, to rust.

Areas of application

Metal balls are used in many different applications; starting from spray cans over valves, level indicators up to belt systems.  However, there are also applications where the ball is more misshapen than spherical, e.g. when used as a weight or as a mixing ball. Steel balls are also used in our ASK ball bearings and in our rod ends with ball bearings.

Technical basics

Balls are normally used as rolling elements in rolling bearings. In addition, however, there are other areas of application, such as in recirculating ball steering systems or as valve balls, etc.


Definitions, terms

G class, ball quality according to ISO 3290 and DIN 5401

Dw nominal diameter of ball

Dws single diameter of a ball. Distance between two parallel planes touching the ball surface.

Dwm mean diameter of the ball lot. Arithmetic mean of largest and smallest individual diameter Dws of a sphere.

DwmL mean diameter of the spherical lot. Arithmetic mean of largest and smallest mean sphere ∆, Dwm in a lot.

IG Grade interval. Amount into which the allowable dimension of the nominal diameter of the ball is evenly divided.

Lot a certain number of balls produced under the same conditions (one machine filling).

Ra Surface roughness according to DIN 4768.

ST Sort tolerance. Range within which DwmL may move within a grade (equal in amount to IG).

tDw Shape tolerance. Deviation from the spherical shape.

VDwA Variation of diameters in a variety. Difference between largest and smallest mean diameter Dwm in a grade. Applies to G500 to G700 and to special balls.

VDwL Variation of diameters in a lot. Difference between largest and smallest mean diameter Dwm in a lot. Applies to G3 to G200.

VDws Difference between largest and smallest single diameter.

Grade Distance of the mean sphere t, of a lot (for VDwL) or of the subset of a lot (for VDwA) to the nominal diameter of the sphere Dw, rounded
to an integral multiple of the grade interval IG.


For G3 to G200 applies:

The lots are assigned to the middle of the grades according to their statistical mean value, i.e. a maximum overhang of    is allowed at both grade boundaries.

In addition, a further overhang of    is possible.

For special balls the following applies: Sorting according to DIN5401


Tolerances of hardened steel balls according to DIN 5401


Tolerances of hardened stainless steel balls to DIN 5401

Tolerances of non-hardenable stainless steel balls to DIN 5401



Hardness and materials








Steel balls