Webster’s Revised Unabridged Dictionary · 1913
Triblet
Trib′let, Trib′o·let, n. [F. triboulet.] 1. A goldsmith's tool used in making rings. Ainsworth.
2. A steel cylinder round which metal is drawn in the process of forming tubes. Tomlinson.
3. (Blacksmithing) A tapering mandrel.