A weapons-grade ring of electrorefined plutonium, typical of the rings refined at Los Alamos and sent to Rocky Flats for fabrication. The ring has a purity of 99.96%, weighs 5.3 kg, and is approx 11 cm in diameter. It is enough plutonium for one bomb core. The ring shape helps with criticality safety (less concentrated material).
http://en.wikipedia.org/wiki/File:Plutonium_ring.jpg
