Lego Technic 60C01 Clutch Gear Bore size
Outer (hub): 6.8 mm/.268 in./ 17/64 in.
Inner (shaft): 4.9 mm/ .193 in./ 25/128 in.
Teeth (key): 3.32 mm/ .1305 in./ 17/128 in. 

-These are close/approximate, not exact due to the tolerances and/or wear. I measured 4 different gears with a digital caliper and the measurements were all within .10 mm of the listed measurements. The measurements even varied slightly within a single gear depending on side and orientation.  

Also, I think you can find the answer to your second question about pitch here: "What is the &quot;Module&quot; of a LEGO gear?"