depth of the concave portion can vary from one eighth of the total height of the seal 20 to seven eighths of the maximum height of the seal 20 in the case of a co molded cap and gasket the maximum depth is not applicable as the division between the cap and gasket is non existent in such an embodiment the maximum depth of the cap can occur at a level above the underside of the cap as shown in fig5 an alternate embodiment includes winged portions 22 and 23 that do not extend beyond the width of the zone of attachment or contact 21 when the seal 20 is in an uncompressed state when such a seal 20 is compressed between the underside 11 of the cap 10 and the bearing or sealing surface 34 the ends 40 and 41 of the winged portions 22 and 23 can extend beyond the width of the zone of attachment 21 as shown in fig6 the walls 48 and 49 extending from the zone of contact 21 to the ends 40 and 41 of the winged portions 22 and 23 can be concave as shown in fig7 8 and 9 the seal 20 can be attached to the barrel or flange 33 instead of the.