It depends on what fit you want and what the manufacturers tolerances are.
This link should help quite a lot
http://www.draughtsman.co.uk/informa...ance_holes.htm.
Also depends what level of detail you want to go into, the more details you use on the drawing the better quality part will come out of it at the end, however this will cost more so there's always a balance.
Is your intent to get them manufactured or just designing them as a training exercise? Which CAD package is it? I work with Inventor and AutoCAD so have quite a bit of understanding with those 2.