Does a plastic plate require tapping? I thought only metal plates and skis with metal layers require it. I have always used a rule of thumb that the 4.1 mm hole is for the metal plate/layer, and the 3.5 for wood cores.
It's actually 4.1mm for metal layers and 3.6mm for wood core. In this case though we're talking about plastic (since the FB has a plastic mounting plate above the steel topsheet). I've used 4.1mm for the plastic plates (to avoid adding additional stress to the plastic). My bindings haven't pulled out yet!