Its made to a standard not a price! And produced by a British company that makes many of its products in good old Horwich!
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Here is something of interest.
Years ago I did a survey of the manufacturers of extruded polymer materials, including monofilaments. The reason for this was to unearth possible requirements for molten polymer filters.
I discovered that regarding monofilaments, there were only a handful of extruders of this stuff in the world, and they were situated in the USA, Germany, Japan and South Korea.
There were no polymer extruders in the UK.
The biggest market for extruded monofilaments by the way is toothbrushes!
Now things may have changed since 1999, the time I did the survey, but at that time there were no polymer monofilament extruders in the Peoples Republic of China. There are now I believe.
Just a point on terminology.
The term "mono" is a short form of monofilament. Monofilaments which cover fishing lines are made from a variety of polymers, including PVDF (one of the fluorocarbons of which there are several).
Monofilaments (single filaments) are produced in very much the same way that a spider produces the silk to make its web. In fact the orifice that the liquid passes through is called a spinneret, be that orifice on a spider or a man made machine. In the case of a machine, the polymer is heated to make it molten, then it is forced by vacuum or pressure through the spinnerets, after which it cools and becomes the final product.
All sorts of adjuncts can be mixed with the basic nylon to create many different kinds of physical properties. Also, temperature variation and speed of extrusion can be applied.
Most of this of course is secret and known only to the manufacturer.