nail, metal pin driven by force applied at one end into pieces of material, usually wood, to join them together. The strength of a nailed joint depends on the properties of the wood, the type and number of nails used, and the type of loads applied to the joint. When the nail is subjected to side loading, the strength of the nail itself also becomes important. Generally speaking, a nail holds better when driven across the grain of a wood than parallel with it and better in a hardwood than in a softwood. However, since a softwood has less tendency to split than a hardwood, more nails can be driven into it. Various means, such as texturing the surface of a nail or coating it with high-friction materials are used to increase its withdrawal resistance.