holds the main body of the cartridge case below the shoulder, and an extension on the right that forms two similar loops which were designed to fit in between the two right-side loops of the next link, and which have a small metal tab that extends down to the cartridge base and fit into the extraction groove of the case. The M13 link binds the rounds from halfway down the length of the case to the case head. This was designed so that the bolt of the machine gun using the link would come forward upon squeezing the trigger and strip a round from its link from below the cartridge, and the round would be chambered, fired then extracted and ejected. The feeding pawl in the gun would pull the belt to the right as the gun was fired or cocked, sending the loose link out to the right side of the receiver, where the expended case was also ejected, normally separately from a different ejector port to the link. MIL-L-45403D stipulates that the force to strip a NATO approved round from the M13 link should be between and the belt have a minimal tensile strength of . A single M13 link weighs approximately . The links often have an extra anti-corrosion surface treatment, generally (oil impregnated) black phosphate, and can be collected and reassembled by hand with fresh ammunition, but in practice this is not commonly done as it is labor-intensive, and the inexpensive links are considered disposable. Sometimes the ejected link pieces are collected to avoid littering the interior of aircraft and vehicles or reuse. The early 1970s M27 link is a link of smaller, but identical design, used among NATO for 5.56×45mm NATO chambered light machine guns, such as the FN Minimi/M249, HK21, MG4, CETME Ameli, K3, Mini-SS and Negev, among others. See also M1 link M27 link List of firearms References http://www.army-technology.com/contractors/ammunition/eurolinks/ M13 link technical data Firearm components Ammunition Military equipment introduced in the 1960s