the best way is to create an attribute for each part number of the drawing parts and then create a block consisting of the attribute and bubble/leader. when you are ready to number the parts of your drawing, insert the block name of the bubble drawing and on the command lines you will be asked to insert part numbers which automatically will replace the attribute within the bubble; then direct the block drawing to the parts to be numbered. Refedit will allow you to modify the block by stretching and directing the leader to the appropriate parts. Make sure you close refedit properly. You must reinvoke the block drawing to number each part of the drawing.
