I'm planning to change the rigid eystrap on my boom with a soft strap made from a bit of cover left over from a tapered spin sheet. I knew of this diagram in the class rules and the 1 inch width rule, but what about the 15mm bit? It says "nominal" on the right of the diagram and is not mentioned elsewhere that I could find. Does that mean it's not actually controlled by the rules and is just a recommendation? It would seem (to me) pedantic for it to be controlled, but there is a measurement in the class rules....