In reply to CurlyStevo:
Steve,
Stevo,
I was speaking to the Grivel distributor the other day about exactly this.
Grivel threads are designed this way so that when loaded the force is spread though the ice at a roughly 45 degree angle from the screw.
This design spreads the force over a greater area of ice - and importantly helps to prevent the ice directly around the screw failing.
IMO - a much better design than the BD thread.
Marek: well done - pretty much bang on!