The Collaborative International Dictionary of English v.0.48:
Triblet \Trib"let\, Tribolet \Trib"o*let\, n.] [F. triboulet.] 1. A goldsmith's tool used in making rings. --Ainsworth. [1913 Webster] 2. A steel cylinder round which metal is drawn in the process of forming tubes. --Tomlinson. [1913 Webster] 3. (Blacksmithing) A tapering mandrel. [1913 Webster]