NEW INFO I WAS SORRY THAT THE MOUNTING BRACKET WILL BE DONE DURING THE RIDE AND I DIDN'T KNOW BY THE DEADLINE! THE VALVE STEM IS NOT DAMAGED BUT I HAVE LOST AIR INSIDE TWICE! BY VISION THIS HAPPENED WHEN THE EXPANSION WAS PUT INTO OPERATION! DO NOT BUY THIS ITEM IF YOU PLAN TO USE IT AS A TWIN EXTENSION ON YOUR CAR! .As? I still don't know. Luckily I only needed one. When I connected another mount, I certainly didn't try to tighten the mounting screw as it should. Hopefully it doesn't come loose when moving. The worst that can happen is that the bracket can come loose and the valve stem can snap through the slam valve extension. Inner tire deflation is not what I want, so I will most likely try to find another way to install an extension or get another one! Certainly not worth the price of the item, at any cost.