In order to restrain the production costs, it is a good norm to avoid adopting narrower tolerance fields than necessary for the real functional use of the parts.
Avoid adopting general indications of fixed and narrow fields for all the dimensions of a drawing; it is better to indicate the precision or quality degree of tolerance, referring to the dimensions where this is applied.
To sum up, the best tolerance field to be achieved with castings is of ±0,7 of the nominal value, with a minimum of ±0,10% mm for the dimensions lower than 15 mm.
On the enclosed table we have indicated the linear tolerances according to the precision degrees required. Please note that we will adopt the following degrees:

- Precision grade D1: For all the free dimensions where an indication of the tolerance is not needed.
- Precision grade D2: For all the functional dimensions, where a defined tolerance is needed.
- Precision grade D3: For all dimensions needing narrower tolerances. It is only applied in particular cases and it is only valid for individual dimensions chosen according to the customer.

See table of dimensional tolerances.