Mitch: The QC gravers aren't square, but onglettes, flats, rounds, etc. The graver has been shortened and the shank ground to fit their QC collets. The thickness of the QC shanks will vary according to graver type, and the height is around 2.7mm. I just measured a few of mine and that's about the average.
thanks for the clarification, Sam. i only have a QC collet in my Monarch hdpc, in which i only use squares, so my mind was stuck in that situation. you're right, a 3/32" sq. will fit comfortably inside a 1/8" circle.