Please help: headmill "inch to milimeter convert

Go to worldwidemetric.com they have a very useful online calculator for future reference. Just click on the calculator tab at the top of the screen.
 
Yeah, but if all say this mill is perfect.. i need to be really specific...

but I dont know if the number 0.889mm is to difficult to do? or I just should stick with 0.88mm 0.8mm or 0.9mm, although 0.9mm is over 0.035"