Attached is a photo of a .012OD x .006"ID  SST hypo tube.  
The window is .005" wide and the pocket on the end is .002" deep 
leaving a .001" floor.  

The features are repeated 4 times around the tube 90° apart.  
There is a tip of a #11 Exacto blade for reference.
Made on a manual Bridgeport clone.

Skuke