The Zastava M84 is a general-purpose machine gun designed and manufactured by Zastava Arms. It is a gas-operated, air-cooled, belt-fed and fully automatic shoulder-fired weapon.
The M84 is a licensed copy of the Soviet Union's PKM, with a few differences such as a differently shaped stock, and a slightly longer and heavier barrel which has slightly different measurements at the gas port and forward of the trunnion in diameter.
The M84 is intended for infantry use, against enemy infantry and light vehicles. It is also configured for tripod mounting (like the PKS).
The M86 is a tank machine gun, and is designed to mount as a coaxial weapon on M-84 tanks and other combat vehicles. The stock, bipod, and iron sights are omitted from this version, and it includes a heavier barrel and electric trigger, much like the Russian PKMT. Another version, the M86A, is designed for external mounts and can be used dismounted.
An improved version of the M84. The changes include a picatinny rail on the receiver and a new buttstock.