Print this out:
http://www.littlemachineshop.com/Ref...DrillSizes.pdf and laminate it and hang it somewhere handy.
There are other useful references on this page:
http://www.littlemachineshop.com/Ref.../reference.php
You can also buy charts at McMaster. Check items 3233T11, 3233T15, 3233T12, 3233T16.