In woodworking and construction, a nail is a small object made of metal which is used as a fastener, as a peg to hang something, or sometimes as a decoration. Generally, nails have a sharp point on one end and a flattened head on the other, but headless nails are available. Nails are made in a great variety of forms for specialized purposes. The most common is a wire nail. Other types of nails include pins, tacks, brads, spikes, and cleats.
A metal nail
Nailor's Workshop King's Norton, an etching by Henry Martin Pope (1843-1908)
Different types of nails: 1) roofing 2) umbrella head roofing 3) brass escutcheon pin 4) finish 5) concrete 6) spiral-shank 7) ring-shank (a used, bent "gun" nail, with barbs left over from the tool's feed system)
Horseshoe nails
A fastener or fastening is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel.
Typical fasteners (US quarter shown for scale)
Structural bolt DIN 6914 with DIN 6916 washer and UNI 5587 nut