This is a used 35mm Hegar Sprag Freewheel hub. It includes instructions, removal/install tools and sprockets from 22-28 teeth. This was used on an Anderson super kart with 35mm axel. This is freewheel hub that gives forward drive but if engine seizes it simply coasts to stop without further destroying engine. It also frees up and unbinds chassis and without engine breaking improves engine life. More info could be found on hegar4 webpage.
Some of these units have lock button for push starting. This does NOT have that so you need to start from engine.