One thing to keep in mind. .008 or .040 is already inches. There are one thousand, thousands in one inch. .008 is eight thousands of one inch. Also .040 is 40 thousands of one inch. To convert a fraction to a decimal, say 1/16th, divide the 1 by the 16 and you will come up with the decimal equivalent. 1/16" expressed as a decimal is .062. Something that my really help is a Starrett tap drill chart, and their metric tools chart. The metric one has a chart that converts all fractions from 1/64th to 1 inch, from fractions to decimals and then to millimeters, in 1/64th increments.

Here is another one. Don't know anything about them. http://www.acpsales.com/OnlineStore.php