Abstract: A device for connecting body members of pressure vessels, such as the covers of nuclear reactor pressure vessels, especially to permit the rapid removal and fitting of lids or covers of such pressure vessels, includes a stud bolt to be mounted in one of the members while passing through an aperture in an adjacent member, the bolt being provided with a head and a clamping nut, a metal member adapted to fit between the adjacent member and the head, and means for heating the metal member to cause expansion thereof against the head to allow tightening and release of the clamping nut.