08/03/2026
TOOLS OF THE CRAFT: TREENAIL (WOODEN PEG)
A treenail, also called a trunnel, is a turned or hand-riven wooden peg driven through a bored hole that passes through an
assembled mortise and tenon joint to lock it mechanically. It is one of the most important fasteners in traditional timber frame
construction and has been used in virtually every culture that built in wood.
What is it used for?
In timber framing, treenails are driven through holes bored simultaneously through the mortised and tenoned members after
the joint is assembled. In drawbored joinery, the holes are offset slightly so that driving the peg draws the joint surfaces
together under tension. White oak is the traditional material because it is hard, dense, and swells with moisture, tightening
the joint over time.
How is it made?
The strongest treenails are riven, meaning split from the log along the grain, rather than turned on a lathe. Riving keeps the
grain fibers continuous through the peg, making it far stronger than a turned peg cut across the grain. A rounder plane is
used to shave the riven blank down to a consistent cylindrical diameter sized to the bored hole.
When was it made?
Treenails predate iron fasteners in woodworking history and appear in some of the earliest surviving timber frame structures
in Europe and Asia. They were the primary fastener in timber frame construction and wooden shipbuilding for centuries.
White oak treenails remain the preferred fastener for major structural joints today because they are strong, they expand with
moisture, and they are entirely consistent with the material they join.