To enable interchangeable fits, component dimensions have to be specified. The degree of accuracy described and the allowances made for variations in the dimensions that will still allow parts to fit together are referred to as the tolerances. Generally, the tighter and more exact the tolerances are then the more likely the fit will always work, but the more expensive it will be to produce with profound effects on costs and therefore product sales. Tolerancing products and components is therefore a balancing act between performance and production.