As an ex firefighter i&＃39;ve seen first hand the need for this carrier. Cylinders are in an upright position at the fire scene thus eliminating damaged cylinders, valves and prevents firefighters from tripping over loose cylinders. An excellent system to sort full and empty air cylinders. This carrier is also used to carry empty cylinders to the refilling station in a secure and safe manner. Many are sold for fire department apparatus floor use by adding industrial casters.This patented product took 3 years to develop and is now being used by fire departments, mining companies, fire extinguisher companies, paramedic units, scuba divers and the military.