treenail breaks or fails but the wood it is fastening remains intact the remaining trenail can be cut out and replaced with a larger treenail that fits snugly. In addition, treenails have the ability to move over time and retain structural integrity. Uses in building structures Early mortise and tenon trusses with spans of less than used treenail fasteners. When used in a truss, the connecting mortises are drilled off center such that when the treenail is inserted it creates a tighter joint. Because of the large number of trenails required in a truss, the treenails can be turned on a lathe with a head and a tapered end, often kept extra-long for the tightest fit. The bottom chord often requires 2–3 pegs and is the weakest part of the truss. Hence the treenail can not prevent failure in spans of over . In cases where significant shrinkage may occur, it may be necessary to use iron U-straps or reinforcements. Uses in ships 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. However, when the treenail was a different wood species from the planking, it usually caused rot. Treenails and iron nails were most common until the 1780s when copper nails over copper sheathing became more popular. As late as the 1870s, the merchant navy ships used treenails and iron bolts, while the higher class ships used the copper and yellow metal bolts and dumps. In the 1870s tradition, treenails were typically used in a ratio of four treenails to one bolt with the exception that sometimes the number of bolts was increased. In later corvettes, the ratio was changed to two treenails to one bolt. Uses in railroads Similar wooden trenail fastenings were used as alternatives to metal spikes to secure railroad rail-support "chairs" to wooden sleepers (ties) in early Victorian times. Treenails were extensively used constructing railroads in North England. References Woodworking Shipbuilding Timber framing