Abstract: A lid is rotatable relative to the upper end of a container. The container carries at least two circumferentially spaced ribs tapered longitudinally in thickness from a relatively narrow rib end to a relatively wide rib end in a given circumferential direction. The lid may have an equal number of lugs, each defining a tapered passageway having a relatively wide end sufficiently large to provide clearance around the relatively narrow end of the corresponding rib and to permit rotation of increments of successively smaller cross section past increments of successively larger cross section of the ribs until the lugs and ribs jam against each other radially, axially and circumferentially to provide a relatively rigid structure where the ribs and lugs overlap. At least three exterior walls of the ribs simultaneously engage three interior walls of the lugs when the ribs and the lugs simultaneously engage. At least one of the jamming surfaces and an engaged surface is in an oblique plane.