Review on J-Chen 4pcs 12-Inch/300mm Stainless Steel Tire Valve Stem Extenders Adaptor for RV Tires Truck Motorhome Coach Pickup Trailer by Dave Russell

They're pretty stiff - good considering they hold over 100psi of air. However, they flex well enough to fit inside the wheel/bonnet. It's not the product's fault, but it could have taken me a little longer for my application. The length of 12 inches hardly fits. Also, I had to replace the included screws with longer versions to effectively tighten them.