The shrinking ring of bubbles encircles the school and confines it in an ever smaller cylinder.

The jacket thickness was reduced by machining at the ends, making a semigroove into which the steel shrink rings fitted.

In small pieces instead of bars the smith sometimes bent a sheet of iron into a cylinder, welded the edges together and shrunk rings around it, as above.

The rebels are now in control of several major towns and the headquarters of a national park where endangered mountain gorillas live in the middle of a shrinking ring of safety.