Grooving tools are a special case. Because of the back clearance on the tool, they cannot be shimmed out and retain the original size.  Thus,  groove tools can only be reground, and the size of the reground insert will be smaller than the original.  This can be done two ways. 

1. We can regrind the insert by the least amount necessary to get a good cutting edge, or 

2. We can grind all tools in a batch to a preset size ( .015”  smaller than original width, for example), and any which don’t clean up at that size are scrap, or are ground to a preset size which is smaller yet.