The grey ones are ultra-stiff.

Upside: Highest performabce
Downside: They shatter if you run them into the ground.

The yellow ones are quite flexible and, as a test, I bent one side of the prop completely in half; wheres the tip of the blade then faced the other tip. The prop did not break.

This is the one we recommend if you want the one least likely to break upon impact.

Although the surface area is smaller, your engine should run at higher RPM, making up for the difference. Here is a link to the product:

http://coxengines.ca/product.php?pro...t=9&page=2

Bernie
www.coxinternational.ca