In small sizes, the compression fitting is composed of an outer "compression nut" and an inner "compression ring" or ferrule (sometimes referred to as an "olive") that is typically made of brass or copper or steel. Ferrules vary in shape and material but are most commonly in the shape of a ring with beveled edges. To work properly, the ferrule must be oriented correctly, in the case of copper olives they are normally barrel shaped and this means they cannot be fitted incorrectly, but where this is not so particularly in Hydraulic and high pressure applications the ferrule is fitted such that the longest sloping face of the ferrule faces away from the nut.