The first consideration when choosing a petcock is to determine which direction the petcock outlet needs to be facing, left side, right side, or vertical. Next you need to know two measurements in order to choose the right petcock for your motorcycle. You need to know the size of the fuel inlet on your carburetor. Typically, you want the same size fuel line going from your petcock to your carburetor. The second measurement is the thread pitch and size for your petcock bung on your gas tanks. Your petcock has to have the same thread pitch and size in order to mount into your gas tank.