Patent ID: 7726483

Claim:
A first cover for a container, the first cover comprising: a first closure portion, a first engagement portion, a central region, wherein the first closure portion is sealingly engageable with a second closure portion of a base so that when the first and second closure portions are engaged with each other, the first cover and the base define a substantially sealed storage area, wherein the first engagement portion is engageable with a second engagement portion of the base the first closure portion comprises locking rings, the locking ring of the first closure portion comprising an inner wall, a retention bead, and an outer wall, and wherein the locking rings include an upper shoulder and a lower shoulder, and each shoulder includes an inner surface and an outer surface; wherein the respective outer walls of two or more first covers are lockingly engageable to one another in a lid stack; and wherein the outer surface of the upper shoulder of a lower first cover fits inside of, and engages with, the inner surface of the lower shoulder of an upper adjacent first cover; and wherein the central regions of two or more first covers are lockingly engageable with one another in a lid stack and the central regions have engagement portions having upper and lower protrusions wherein the upper and lower protrusions are convex on one side and concave on the other side.