These caps are made to keep your regulator attached while you are not using it. They are typically used with a High Pressure hose to go from the cylinder to the regulator mount. Regulators don't ride directly on the cylinders, they are mounted elsewhere and connected via hose. These caps make it so that you don't have to disconnect and put the standard cap back on the cylinder while in motion. Please specify for oxygen or acetylene in the purchase comments.
