I've got a set of questions for the distinguished body.
     
     It regards to specifying the finished diameters of non-plated holes on 
     PCBs.  
     
        1.  What is the tightest finished hole size tolerance I can 
     reasonably specify for volume production.  Is this a function of hole 
     size.
     
        2.  I have a standard table of drill bit sizes.  Does the PCB 
     industry have custom drill bit sizes or are these all in the 
     standards?  If there are custom sizes are these published anywhere?
     
        3.  For a given drill bit size, what will be the nominal finished 
     hole size drilling in a typical FR-4,.062" thick PCB?  
     
        4.  Is there a table of the different values of nominal FINISHED  
     holes sizes for non-plated through holes.
     
     My problem is that often I need to specify tight tolerance holes and I 
     need to know the "sweet spots" of finished hole sizes for these holes.
     
     For example I might desire to specify a hole .093" +/- .001", not 
     knowing that there is no drill size near this size.  Or if there is a 
     drill size, I might not know that if I drill at a given size the 
     finished hole shrinks slightly.  I need to understand this to 
     understand the "sweet spots" for tight tolerance hole sizes.
     
     I'd appreciate any feedback.
     
     Thanks,
     
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