In general, a zero-value tolerance represents an unmanufacturable condition and is not allowed.

In general, the tolerance value specified for a geometric tolerance should be greater than zero. An exception where a zero-value tolerance is acceptable is a geometric tolerance (e.g., position) which has a Ⓜ or Ⓛ tolerance zone material condition modifier applied. In that case, the tolerance zone includes a bonus tolerance as the feature departs from its specified condition.

To eliminate this problem, you should either change the tolerance to a non-zero value or in the case of a zero-value geometric tolerance, specify a Ⓜ or Ⓛ tolerance zone material condition.

ASME Y14.41-2019 (par. 9.2.3) states that 'a displayed feature of size dimension shall always include a tolerance.' Thus, size dimensions must always have a tolerance specified (i.e., may not be shown as 'nominal') and the specified tolerance range must be greater than zero.

An exception to this requirement is stock size dimensions. Tolerances are not required (but are permissible) for stock size dimensions (see ASME Y14.5-2009, par. 1.4a or ASME Y14.5-2018, 4.1a). Keep in mind that Rule #1 does apply to stock size dimensions (i.e., no form tolerance prescribed by limits of size). However, if no form control is explicitly specified, the applicable industry or government standard typically prescribes the limits for straightness, circularity, and other geometric characteristics. See ASME Y14.5-2009, par. 2.7.2 or ASME Y14.5-2018, par. 5.8.2 for more information.

Tolerances are also not required for reference dimensions, although they are permissible.

The specified tolerance range for all non-size dimensions (e.g., offsets and angles) must be greater than zero. ASME Y14.41-2019 does not explicitly require a specified tolerance for non-size dimensions, so this message does not appear for non-size dimensions that are shown in their nominal state. However, it is good practice to explicitly specify tolerances for all dimensions.