160 hits for your term -- try to find a definition. Seems pretty 'variable' including in your text. Since you're talking about tolerance, you seem to want something else. But your term seems to be misused here.

Search 'allowance' + 'dimension' and find some reading, including at https://en.wikipedia.org/wiki/Allowance_(engineering)

No need for two words to describe 'allowance,' esp. in your context.

"A tolerance is the limit of acceptable unintended deviation from a nominal or theoretical dimension. Therefore, a pair of tolerances, upper and lower, defines a range within which an actual dimension may fall while still being acceptable.

In contrast, an allowance is a planned deviation from the nominal or theoretical dimension."