When I got my G3 Onyx Bindings the Onyx crampon had yet to be released. Thus I had to look else where for my crampon needs. I knew that not all cramps attached to the binding; some attach directly to the ski. From some searching I found B&D Crampons . Looking at their website I did not see a set up intended for the G3 Onyx. So I contacted Bill Bolllinger at B&D ski gear for some help. Do not confuse B&D with Black Diamond, which is often referred to as BD. Bill sent me out some parts and soon I was out in the shop doing some crampon fitting.
My initial trail had me using the plastic block spacers. However when on the top climbing bar, the crampon would not engage the snow. Thus the taller post is required. Even with the taller F1/F3 spacer the crampon does not engage the snow to its full depth. I do not believe that the Onyx bindings are any taller than Dynafit. Due to the mounting tab set further back, the crampon contacts the boot at the arch or the highest location of the boot. This is similar to what happens when you run a F1/F3 style boot and B&D crampon set up.
An alternative to using a boot contacting spacer on the crampon is to use a crampon lock. The lock fixes the cramp onto the deck of your skis. This provides the maximum contact of the crampon with the snow/ice. Because the crampons is fixed on the ski, they are not allowed to hing. This results in you having to lift the ski with each step instead of gliding the ski along on the snow. If your bindings do not have a clear shot of the deck between the toe and heel pieces, you can mount the crampon in front of or behind the binding with the lock to hold it down. This allows a large degree of verisitlity with a difficult to set up crampon binding combo.
Ski crampons are a personally must for me. I tend to carry them on every back country ski outting I go on. I find that they provide the much needed grip in icy situations and even help me gain some purchase when it is steep and slushy. So the next time you are headed out into the backcountry, leave the American Express at home, but make sure to pack your ski crampons with you!