Gimbal for a SteadiCam

This is a Gimbal designed for a DIY SteadiCam that I made for a colleague at work (See http://www.yb2normal.com/DIYsteadicam.html).

It makes use of two 624 bearings in addition to the required 608 bearing.
It would also be possible to use four 624 bearings or to use no 624 bearings. I thought using two was a good compromise. If you decide to use no 624 bearings then the height of the middle ring can be reduced to 16mm (same as the outer ring) or even 12mm.