According to the 1913 Luger P.08 blueprints, the tool is 50.5 mm long with a tolerance of -1mm and no positive tolerance.
The tool should be 24 mm wide with a tolerance of + or - 0.5 mm.
The thickness is spec'ed at 2.5 mm (with no tolerance).
The screwdriver tip is 7 mm wide (with no tolerance), and the ground screwdriver end is 6.5 mm (with no tolerance).
If anyone would like a complete set of these blueprints on CD, Check the "for sale forum" for the sticky at the top... They are a real handy reference just for things like this...and a bargain at the price for the information they contain.
Here is a SMALL extract (reduced 50% twice) of the blueprint page containing the tool.