Barbed wire, also known as barb wire, less often as bob wire or, in the southeastern United States, bobbed wire,is a type of steel fencing wire constructed with sharp edges or points arranged at intervals along the strand(s). It is used to construct inexpensive fences and is used atop walls surrounding secured property. It is also a major feature of the fortifications in trench warfare (as a wire obstacle).
A person or animal trying to pass through or over barbed wire will suffer discomfort and possibly injury. Barbed wire fencing requires only fence posts, wire, and fixing devices such as staples. It is simple to construct and quick to erect, even by an unskilled person.
Barbed wire was the first wire technology capable of restraining cattle. Wire fences were cheaper and easier to erect than their alternatives. (One such alternative was Osage orange, a thorny bush which was time-consuming to transplant and grow. The Osage orange later became a supplier of the wood used in making barb wire fence posts. When wire fences became widely available in the United States in the late 19th century, they made it affordable to fence much larger areas than before. They made intensive animal husbandry practical on a much larger scale.
Barbed wire fences remain the standard fencing technology for enclosing cattle in most regions of the US, but not all countries. The wire is aligned under tension between heavy, braced, fence posts (strainer posts) and then held at the correct height by being attached to wooden or steel fence posts, and/or with battens in between.
The gaps between posts vary depending on type and terrain. On short fences in hilly country, steel posts may be placed every 3 yards (2.7 m), while in flat terrain with long spans and relatively few stock they may be spaced up to 30 to 50 yards (46 m). Wooden posts are normally spaced at 11 yards (10 m) (2 rods) on all terrain, with 4 or 5 battens in between. However, many farmers place posts 2 yards (1.8 m) apart as battens can bend, causing wires to close in on one another.
Barbed wire for agricultural fencing is typically available in two varieties: soft or mild-steel wire and high-tensile. Both types are galvanized for longevity. High-tensile wire is made with thinner but higher-strength steel. Its greater strength makes fences longer lasting because it resists stretching and loosening better, coping with expansion and contraction caused by heat and animal pressure by stretching and relaxing within wider elastic limits. It also supports longer spans, but because of its elastic (springy) nature it is harder to handle and somewhat dangerous for inexperienced fencers. Soft wire is much easier to work but is less durable and only suitable for short spans such as repairs and gates, where it is less likely to tangle.
In high soil-fertility areas where dairy cattle are used in great numbers 5- or 7-wire fences are common as the main boundary and internal dividing fences. On sheep farms 7-wire fences are common with the second (from bottom) to fifth wire being plain wire. In New Zealand wire fences must provide passage for dogs since they are the main means of controlling and driving animals on farms.
Sources – Wikipedia