skirt 18 is integrally joined to the inner skirt 17 by a circumferential web 21 the inner skirt wall 17 is conical to the same or a lesser degree than the outer skirt 18 in an opposite direction from the outer skirt 18 so that it decreases slightly in diameter in a direction toward the central disc portion 16 the central disc portion 16 and concentric skirts 17 18 all have substantially the same wall thickness the plane of the main body of the central disc portion 16 extends forwardly of a lead edge 22 of the outer skirt 18 at its forward end the inner skirt turns radially inwardly to provide a flared surface 25 for piloting the cap 12 onto the shell 11 as indicated the flared surface 25 is offset at its inwardmost point radially a distance from the nominal outside diameter of the inner wall 17 a distance at least equal to the nominal wall thickness of the shell 11 the radially inward side of the forward end 22 of the outer skirt wall 18 is beveled at 26 to increase the inner diameter of the outer skirt wall at this point for facilitating entry therein of the shell end designated 27 the cap 12 is fully positioned on the shell when the shell edge 27 abuts the web 21 which thereafter axially restrains further inward cap movement the closure tape 13 is coated on its inner face with a pressure sensitive adhesive and is shrinkable upon application of heat a suitable.