Treenails or Trunnels
Treenails were used as fasteners for shipbuilding. They were often made of locust wood. They were less expensive than bolts for fastening, and they made tight connections. The treenail is like a large dowel, pounded into a hole drilled through the pieces of wood to be fastened together, and set by pounding wedges into both ends, so that the treenail will not come out. Treenails were often called "trunnels."
This image is from Basil Greenhill and Sam Manning, The Evolution of the Wooden Ship, 1988, p. 145. Used by permission of the artist, Sam Manning.