Like it or not, but if you want to stay in business you better learn to use the "ISO (DIN/ISO 286) System of Limits and Fits". In case your work is all in inches take a look at a newer edition of the MHB. Not only is it easy to use but it will be of great help to you in determining what tolerance to use to achieve a certain fit i.e. Sliding Fit, Press Fit etc..