Abstract: The body member and cover member of a pressure cooker are adapted to be held together by means of inter-engageable pairs of lugs arranged on each member. One or more selected pairs of lugs are constructed so that a shoulder on a first lug or lugs can interact with either of two linearly arranged projections carried by a second lug or lugs. The interaction of the selected pair of lugs produces two locking positions of the body and cover. The pressure cooker preferably incorporates a further safety mechanism, such as a gasket off-set device which prevents pressurization of the vessel if there is only partial overlap of the body and cover lugs.