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A replica of Norfolk held together with trunnels.
Plank fixing, trenails and red lead paint, Qui Nhơn, Vietnam.

A treenail, also trenail, trennel, or trunnel, is a wooden peg[1] pin, or dowel used to fasten pieces of wood together, especially in timber frame construction and wooden shipbuilding. It is an ancient technology. Covered bridges in the U.S. often use treenails as fasteners. Many such bridges are still in use. Locust is a favorite wood when making trunnels in shipbuilding due to its strength and rot resistance and red oak is typical in buildings.

A method of firmly securing such a fastener in shipbuilding was to cut a parallel peg of a softer wood, and then expand its outer end with a wedge of much harder wood driven into it called a foxtail wedge.

Ancient shipbuilding used treenails to bind the boat together. They had the advantage of not giving rise to "nail-sickness", a term for decay accelerated and concentrated around metal fasteners. Increased water content causes wood to expand, so that treenails gripped the planks tighter as they absorbed water. Similar wooden trenail fastenings were used as alternatives to metal spikes to secure rail-support "chairs" to wooden sleepers in early Victorian times.


  1. ^ Edwards, Jay Dearborn, and Nicolas Verton. A Creole lexicon architecture, landscape, people. Baton Rouge: Louisiana State University Press, 2004. Print. 237.