'Common' is a relative term. Howver, I don't see any harm in using the abbreviation as long as you define it in the document (preferably in a list of abbreviations, but at least when it is first used, and perhaps elsewhere if necessary to avoid ambiguity).

--------------------------------------------------
Note added at 28 mins (2007-02-23 14:38:20 GMT)
--------------------------------------------------

Usage of abbreviations in drawings is a special case; it's often unavoidable for practical reasons (space constraints). However, the abbreviations should be explained in some easily recognised location for the benefit of the reader unless the readership cah be assumed to be familiar with them (which can probably best be judged by your client if it is a direct client).