A chain link mould is used along with a mithril bar and a silver bar in a furnace to make a silvthril chain. The mould is obtained during the Legacy of Seergaze quest. If it is lost, another may be obtained from a crate in the Myreque Hideout in Meiyerditch, in the room east of the entrance ladder. Drakan's medallion provides a convenient teleport to the hideout. A chain link mould can be stored in the Toolbelt.
A silvthril chain, as well as a Silver sickle(b) and a Rod of Ivandis, is one of the parts of an Ivandis flail.