My inspiration came from the thing http://www.thingiverse.com/thing:4391 but I'd like one more compact.It is designed with/for : 608 Ball Bearing (diameter of the pink axe is 8mm) 4mm bolts and nuts 8mm threaded shaft with 2 nuts The Bolts between inner and middle ring must be XXmm long (the best length will be add soon) The Bolts between the middle and the outer ring must be XXmm long (the best length will be add soon) The Bolt for handle must be XXmm long (the best length will be add soon)