Parachute cord, also known as paracord or 550 cord, is a type of lightweight and durable nylon rope. This type of cord was originally used for parachute suspension lines, which is where it gets its name. However, the cord is now used for a variety of diverse applications, including in the military.
A US Military standard (MIL-C-5040H) was developed that specifies a number of different types of parachute cord. The standard has been inactive since 1997, but the types of parachute cord it specified are still used as a reference point.
There are four major types specified (I-IV) as well two other variants of types I and II (IA and IIA). Type IV has the greatest number of core or kern yarns, as well as the highest requirement for minimum strength; type I has the fewest yarns and allows the lowest minimum strength. The IA and IIA variants differ from their type I and II counterparts in that both A variants have no core. IIA has a lower specified minimum strength than II as a result (225 lb instead of 400 lb), but IA actually has a slightly higher minimum strength than type I (100 lb instead of 95 lb). All of the types specified are required to have a minimum elongation of 30%.
The colloquial name “550 cord” actually refers only to type III military specified parachute cord. The name comes from the fact that type III parachute cord is specified to have a minimum strength of 550 lb. Since the standard is no longer active, commercially sold parachute cord often deviates slightly or significantly from that produced for military use. Even if commercial cord types are built to meet the military specification’s standards for minimum strength and number of core yarns, commercial cord will sometimes use only two nylon fibers in each yarn, while military cord uses three. The specification also allows for some variance in the number of core yarns used; commercial cord will often use the minimum number unless it is explicitly marketed with a greater number of core yarns (e.g. type III would have 7 yarns unless specifically sold as 9-yarn type III). Since commercial cord is usually still tested to the same minimum strength, these differences can actually prove convenient for personally or commercially used parachute cord, since the lower number of yarns and total fibers can help reduce the thickness of commercial cord.
By Brian Greenlee
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