SKF steel balls: diameters and grades

In RB-3/G10, RB names the line, 3 is the diameter in millimetres and G10 the grade. RB-6/G10 is a 6 millimetre ball of the same grade. Many diameters have decimals because they come from inch sizes: RB-3.175/G20W is a one-eighth inch ball, and RB-7.144/G16 a nine thirty-seconds one.

The grade indicates the precision of form and size: the lower the number, the more precise the ball. The letters that go with the grade or the diameter distinguish the execution or the material, and are copied. Two balls of the same diameter and a different grade are not mixed in the same set.

In a set of balls, all must be from the same lot or, at least, of the same grade and diameter sorting. A ball slightly larger than the rest carries the load alone and gets marked; a smaller one does no work. That is why, when one breaks, the whole set is replaced and not the single piece.

The material matters too. A bearing steel ball rusts if it works wet, and for those cases there are stainless balls or balls of other materials. If the ball acts as the closing element in a valve, the hardness of the seat and the fluid define the choice as much as the diameter.

Send us the complete designation and the number of balls. If you do not have it, measure the diameter with a micrometer, not a caliper, and give us the reading to three decimals. Tell us what they are used for, how many the set takes and whether they work with water, oil or another fluid. If they are spares for a bearing, state its designation.