Captain America Shield Keychain

That round shield is one of the most recognisable shapes in comics, and it shrinks to keyring size better than almost any other superhero prop. Concentric rings closing on a central star is a form that stays legible however small it gets, which is why it works on a set of house keys and not just on a display stand. Keychains are the small change of 3D printing. They are quick wins, stocking fillers and party-bag gifts, the sort of thing people are pleased to be handed and happy to take a spare of. Painted up or left plain, the ring pattern carries the whole design on its own. It also gives a fan who already owns a shelf of larger pieces something to actually carry about — the same emblem as the display model, sized for a pocket.