The principle of wire fences is that they are supported mainly by tension, being stretched between heavy strutted or guy-wired posts at ends, corners, and ideally at intervals in longer stretches (every 50 to 300 metres, 150 to 1000 feet). Between these braced posts are additional smaller wooden or metal posts which keep the wires spaced and upright, usually 3 to 6 metre (10 to 20 feet) apart, depending on the style of fencing used.
Traditionally, wire fencing material is made of galvanized mild steel, but galvanized high-tensile steel is now also used in many places. To prevent sagging of the fence, which raises the risk of entanglement or escape, the wire is tensioned as much as the material will safely allow during construction by various means, including a hand-operated "wire stretcher" or "fence stretcher" (called a "monkey strainer" in some areas) or other leverage devices, a winch, or even by carefully pulling with a tractor or other vehicle.
Wire fences are typically run on wooden posts, either from trees commercially grown in plantations or (particularly in the American West) cut from public lands. When less expensive or more readily available than wood, steel T-posts or star posts are used, usually alternating every 2 to 5 steel posts with a more stable wood post. Non-electrified wire is attached to wooden posts using fencing staples (for intermediate posts, these are fitted loosely, not gripping the wire). Non-electrified wire is held on T-posts by means of wire "clips" made of smooth galvanized wire that wrap around the back of the post and hook onto the wire on either side of the post.
Other than in a truly desert climate, use of rot-resistant wooden posts or steel posts is advised. In the United States, wood with natural rot resistance, such asoak and juniper, was often used until it became in short supply in the 1950s. Then, chemically treated pine and spruce posts became prevalent, and these are also widely used in Britain, together with chestnut. Creosote, pentachlorophenol, and chromated copper arsenate are all widely used in the US and elsewhere for treatment (although some of these chemicals are subject to legal controls).