I would do it like this.
Does it make sense? Not writing a, b, x and y literally of course, but using whatever are the required predefined values.http://files.engineering.com/getfile.aspx?folder=bba1e78f-6be7-447d-b672-a16a47530aa2&file=taper_callout.pdf
I think the most straightforward thing to do would be to simply dimension both openings and specify tolerances on each that do not overlap each other; only one of the openings can be larger than the other and not the other way around. This would be if you only care about the top and bottom...
I can think of two more:
- Holes that are fitted with alignment spring pins. Since the width of the spring pin is narrower with a smaller fastening hole, there will be more clearance and therefore a greater positional tolerance with the mating alignment hole.
- Shaft-to-bore sealing grooves...
