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Parachute cord (also paracord or 550 cord) is a lightweight nylon kernmantle rope originally used in the suspension lines of US parachutes during World War II. Once in the field, paratroopers found this cord useful for many other tasks. It is now used as a general purpose utility cord by both military personnel and civilians. This versatile cord was even used by astronauts during STS-82, the second Space Shuttle mission to repair the Hubble Space Telescope.
The braided sheath has a high number of interwoven strands for its size, giving it a relatively smooth texture. The all-nylon construction makes paracord fairly elastic; depending on the application this can be either an asset or a liability.
While the U.S. military has no overall diameter requirements in its specifications, in the field 550 cord typically measures 5⁄32 inches (4 mm) in diameter.
Military usage 
Despite the historic association of pararopes with Airborne units and divisions, virtually all US units have access to the cord. It is used in almost any situation where light cordage is needed. Typical uses include attaching equipment to harnesses, as dummy cords to avoid losing small or important items, tying rucksacks to vehicle racks, securing camouflage nets to trees or vehicles, and so forth. When threaded with beads, paracord may be used as a pace counter to estimate ground covered by foot. The yarns of the core (commonly referred to as "the guts") can also be removed when finer string is needed, for instance as sewing thread to repair gear, or to be used as fishing line in a survival situation. The nylon sheath is often used alone, the yarn in the core removed, when a thinner or less elastic cord is needed such as when used as a boot lace. Ends of the cord are almost always melted and crimped to prevent fraying.
US Military issue paracord is specified by MIL-C-5040H in six types: I, IA, II, IIA, III, IV. Types IA and IIA are composed solely of a sheath without a core. Type III, a type commonly found in use, is nominally rated with a minimum breaking strength of 550 pounds, thus the sobriquet "550 cord".
The US military specification for paracord outlines a number of parameters to which the final product must conform. Although it contains specific denier figures for the sheath strands and inner yarns, there are no overall diameter requirements for the cord itself. Below is a table of selected elements from the specification.
|Type||Minimum strength||Minimum elongation||Minimum length per pound||Core yarns||Sheath structure|
|I||95 lb (43 kg)||30%||950 ft (290 m; max. 1.57 g/m)||4 to 7||32/1 or 16/2|
|IA||100 lb (45 kg)||30%||1050 ft (320 m; max. 1.42 g/m)||<no core>||16/1|
|II||400 lb (181 kg)||30%||265 ft (81 m; max. 5.62 g/m)||4 to 7||32/1 or 36/1|
|IIA||225 lb (102 kg)||30%||495 ft (151 m; max. 3.00 g/m)||<no core>||32/1 or 36/1|
|III||550 lb (249 kg)||30%||225 ft (69 m; max. 6.61 g/m)||7 to 9||32/1 or 36/1|
|IV||750 lb (340 kg)||30%||165 ft (50 m; max. 9.02 g/m)||11||32/1, 36/1, or 44/1|
The Type III Specification is calculated using the value of 14.0625 feet per ounce.
Civilian availability 
The same properties which soldiers appreciate in paracord are also useful in civilian applications. After World War II parachute cord became available to civilians, first as military surplus and then as a common retail product from various surplus stores and websites. While some commercially available paracord is made to specification, even when labeled as such a given product may not correspond exactly to a specific military type and can be of differing construction, quality, color, or strength. Particularly poor quality examples may have significantly fewer strands in the sheath or core, cores constructed of bulk fiber rather than individual yarns, or include materials other than nylon.
Paracord has also been used by many since the 1970s for whipmaking. The durability and versatility of this material has proved beneficial for performing whip crackers and enthusiasts. Since nylon doesn't rot or mildew, it has become known as an all-weather material for whipmaking. Nylon whips have grown in popularity over the last few decades, more so in the last several years.
Hikers and other outdoor sports enthusiasts sometimes use "survival bracelets" made of several feet of paracord which is woven into a compact and wearable form. Such bracelets are meant to be unraveled when one needs rope for whatever purpose—securing cargo, lashing together poles, fixing broken straps or belts, assisting with water rescues, controlling bleeding with a tourniquet, etc.
Another use of parachute cord is in the stringing of mallet percussion instruments, such the xylophone, marimba, or vibraphone.
Additional uses for parachute cord is in the manufacture of additional items, such as lanyards, belts, dog leashes, and key chains. This is becoming more popular as crafters are discovering this unique material.