Just slightly larger than the M2, the M4 medical oxygen cylinder is a great solution for anyone who needs a convenient, easily transportable medical oxygen supply for a short amount of time. This cylinder weighs under 3 pounds and is only 12 inches in length. Using the RESOURCE v.2 pneumatic conserving device this cylinder can supply just under 5 hours of oxygen or just under 11 hours using the SOLO2 pneumatic conserving device. This cylinder comes standard with a CGA870 medical post valve but can be fitted with a toggle valve, a "Z" valve, a handtight valve ,a handtight and gauge valve, or a CGA540 valve. Select your choice below.