In cases where universally matchable bearings or matched bearing sets are used, preload is determined at the factory during production. In some cases, however, it may be necessary to optimize the preload to accommodate operating conditions. In these cases, the bearings should not be modified, as this requires special tools, and knowledge, and the bearings could be damaged irreparably. Bearing modification should be entrusted exclusively to SKF Spindle Service Centres. It is possible, however, to increase or decrease preload by using spacer rings between the bearings (fig). By grinding the side face of the inner or outer spacer the preload in the bearing set can be changed.

The table provides information about which of the equal-width spacer ring side faces must be ground and what effect it will have. The table and the table contain the necessary dimensional deviation for the overall width of the spacer rings.