A chain is a series of metal links, used for binding or pulling. It is found in the arms of von Bueningen, c.1370 [Gelre 109]. The usual heraldic depiction of chain is with square links, but round-linked chains are found in period; the links’ actual shape is a matter of artistic license. (Indeed, the same effect is often blazoned as, e.g., “annulets interlaced in fess”.)
There seems to be no default orientation for chain; it must be specifically blazoned, e.g., a “chain fesswise” as in the illustration. A chain throughout may also be blazoned as an ordinary of chain, e.g., the “saltire of chain” in the arms of Elwett, c.1460 [RH].
The Order of Knighthood bears: A circular chain.
Guy of Alderney bears: Gyronny sable and argent, a saltire of chains vert.
Éimhín mac Ultáin bears: Per bend sable and argent, a bend of chain Or.