N.A.T.O. The defensive military alliance formed in 1949 by ten european countries. WARSAW PACT A military alliance formed in 1955 by the Soviet Union Netherlands. Norway.
Tank Rings. Tank rings filled with gravel lift the tank above the surrounding grade. This keeps the tank out of standing water and increases the life of the tank bottom.
Piston rings are the ones that completely seal out the cavity formed between the piston and the cylinder. The above picture is the cross-section of a four-stroke IC engine of an automobile. the black colored bands that are present on the piston are the piston rings.