nail

Nail is a term with more than one meaning in common use. It most commonly refers to two unrelated objects: a hard keratin plate on the dorsal surface of the fingers and toes, known as a nail, and a metal fastener used in construction, also called a nail. Both senses derive from different origins, but in everyday language the word is usually understood from context.

The human nail consists of a nail plate formed from keratin, a nail bed beneath, a matrix that produces most of the nail, a lunula indicating growth, and surrounding cuticle and skin. Fingernails grow faster than toenails, typically about 2–3 mm per month for fingernails and roughly 1 mm per month for toenails, with variation by age and health. Nails protect fingertip tissue, aid in manipulating small objects, and provide a rough surface for tactile feedback. Care includes trimming, filing, and avoiding trauma; nails may develop conditions such as infections, onychomycosis, or psoriasis.

A hardware nail has a slender cylindrical shank, a sometimes broad head, and a pointed tip. It is driven into materials by a hammer or nail gun. Nails are made of steel or other metals and may be galvanized, stainless, copper, or aluminum to resist corrosion. Common variants include the common nail, finishing nail, brad, roofing nail, and masonry nail; ring-shank nails provide extra holding power. Nail dimensions are described by length and gauge. They are used to fasten wood, plywood, and other materials, forming joints, frames, and structures.

Machine-made nails became common in the late 18th to early 19th century, enabling mass production and standardized sizes.