Adjustable spanner
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An adjustable spanner, shifting spanner, shifter, crescent wrench or adjustable-angle head wrench (American English) is a tool which can be used to loosen or tighten a nut or bolt. It has a "jaw" (the part into which the nut or bolt goes) which is of adjustable size, which allows for different size nuts and bolts to be handled by the same spanner. Compare this to the ordinary spanner which has a fixed size.
There are many forms adjustable spanners, from the taper locking spanners which needed a hammer to set the moveable jaw to the size of the nut, to the modern screw adjusted spanner.
There is a class of adjustables that automatically adjust to the size of the nut. The most modern are digital types that use sheets or feelers to set the size, and other simpler models that use a serrated edge to lock the moveable jaw to size.
It is uncertain who invented the adjustable spanner. Some early spanners were invented by Edwin Beard Budding (1795-1846) using a screw to replace the wedge that fixed the jaw of a known type of adjustable spanner, and Johan Petter Johansson of Sweden in 1892 using a screw to adjust and fix the jaw.[1] In addition a type called a monkey wrench is thought to have been patented by one Charles Moncky.
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[edit] Proper use
This tool is often misused, causing excess wear or distortion. When the type illustrated is used for heavy loads such as to break loose a nut or bolt, or for final tightening, the movable jaw should always lead the direction of rotation. Failure to do so will cause the movable jaw to become bent and/or loose. (In the illustration the wrench is set up to tighten a right hand thread, using a clockwise motion)
Another school of thought claims that the spanner should always be used with the fixed jaw leading the direction of rotation. The force on each jaw is always the same (equal and opposite forces) regardless of the direction of rotation. However, if the fixed jaw is leading, then the force will be applied to the movable jaw at its base, which will minimise the bending stress on it.
The movable jaw should be snugly adjusted to the nut or bolt head in order to prevent rounding. This type of wrench should never be used on a rounded off nut, as this can overload the movable jaw. Nor should the wrench be used "end on" in cramped quarters, where a socket wrench is more appropriate.
[edit] Genericized trademark
In the US, the term crescent wrench is often used by the general public as a generic term to indicate any adjustable spanner. It is however a brand name owned by the company Cooper Hand Tools [2]. In some parts of Europe they are often called a bahco, which is a genericized trademark as well.:[1]
[edit] References
- ^ a b Swedish Bahco leaflet about the development history of adjustable spanners (including photo’s)
- ^ Homepage of Cooper Hand Tools
