The M13 link, formally Link, M13, is the U.S. military designation for a disintegrating metallic link specifically designed for belt-fed firearms and rounds; it was introduced in the mid-20th century. It is the primary link type for the U.S., and among NATO for the 7.62x51mm cartridge. It has been in use for over 50 years as of 2007 and is used on the Dillon M134D Minigun, M60 Machine Gun, FN MAG, AA-52, HK21, and the MG3, among others.
The left side of a single link had a semi-circular loop which would hold the main body of the cartridge case below the shoulder, and an extension on the right that formed two similar loops which was designed to fit in between the two right-side loops of the next link, and which had a small metal tab that extended down to the cartridge base and fit into the extraction groove of the case. Unlike the older M1 link which bound cartridges to each other at the neck, the M13 bound the rounds from half way 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.
The M13 link replaced the M1 links used on the older M1917 Browning machine gun and M1919 Browning machine gun family, though some conversions of the M1919 to the M13 were done, such as on the U.S. Navy Mark 21 Mod 0 machine gun, which saw service in the Vietnam War. Once converted it cannot use other link types, as firearms made for the M13 Link are not backward compatible with the M1 link (or other systems). The M27 link is a link of smaller scale but identical design used for 5.56x45mm caliber machine guns, such as the M249 SAW
In West German service the link received the designation DM-13. Some other countries also redesignated it when it was adopted.