The Tank Halo is a thermoplastic rubber foot ring for standard cylinders. Protects your car and floor surfaces from the rust and grime that builds up on cylinders. Halo also provides the benefit of providing the space and improved wireless range when used with a standard sensor. So pick one up as a replacement for lost or in addition to the aluminum spacers that are provided with sensors. With or without a sensor, the Halo is a nice accessory for any propane cylinder user.