The Pleter 91 was developed in August 1991 on behalf of the Croatian Ministry of Defence. Production officially commenced in October, with an estimated 100 units being produced per day. It was sold commercially to civilians and used extensively by Croatian militias during the Yugoslav Wars. An integrally suppressed variant, known as the Prigušen, was also produced in small numbers.
The Pleter heavily copied characteristics seen in the Sten, such as a removable barrel assembly, a very similar bolt and recoil spring assembly, and an open bolt firing mechanism, in spite of a vertical magazine instead of a horizontal magazine. The weapon is also said to be quite heavily based on the Belgian Vigneron. Early prototypes had a wooden pistol grip, but the pistol grips on production models were made out of plastic. The weapon had a simplified barrel assembly when compared to the Sten, fixed with an inbus screw.
To further simplify construction of the weapon, it was decided that a fire mode selector and a safety be omitted from the design, making the weapon only have a simple sear-spring-trigger combination. The weapon fires from an open bolt at 630rpm. The Pleter has fixed sights. The magazine well was modified to fit an Uzi magazine, which is easier to load than the magazines used in a Sten and are less prone to jamming.
- The Pleter was named after the town of Pleternica in Slavonia, Croatia, where the OROPLET factory, the factory which produced the Pleter 91, was based.