The Excellon and Sieb & Meyer drill formats are designed to drive CNC drilling and routing machines. They are broadly
similar, differing only in minor details.
Each drill file requires a separate tool-file giving the diameter of the tool ( in some cases the tool-file is embedded in the header of the drill file).
Your drill file should always show the finished hole-size you require.
A drill file without embedded tool sizes looks like this:
A drill file with embedded tool sizes:
- INCH/METRIC defines the unit
- T01 is the tool number
- C indiates that the text numbers are the drill sizes :
00.020 = drill size 0.020″ or 20 mil or 0.50 mm.
More information on the Excellon format is available on Wikipedia.