Most often bean threshing is performed with grain combines and then damage may be as high as 20 to 50%. The main unit in grain combine causing the damage to beans is the threshing assembly. As can be seen from numerous research studies, the share of the threshing unit in the total damage caused in beans during threshing operation is about 63.0-68.0%. Therefore, studies were intitiated in order to limit the mechanical damage to beans during harvest. The guilding assumption was that mechanical damage can be reduced mainly by tailoring the threshing unit design to the threshed bean and through performing the threshing operation at an optimum bean moisture content. Among many tested threshing-unit designs, the best results were obtained in the multi-drum peg set. The basic idea for its operation consisted in combining the threshed mass with pegs of three revolvin drums. Three varieties of beans, significantly varrying in bean size, were subjected to threshing. Measurements were run at various bean moisture content (15.5-24.5%). Macro- and micro-damage in seeds was evaluated, as well as the quantity of unthreshed beans. Such factors affecting threshing quality as the speed of threshing drums, relative positioning of pegs, drums and the beater plate, as well as the threshing capacity of the units were taken into account during measurements. Results showed that the threshing unit uder study provided high-low seed-moisture levels (15.0-16.5%). The lowest losses were obtained when beater-plate pegs were fully extended at an angle of 10 deg and drum pegs slanted at 30 deg. The optimum speed of the threshing drum for tested beans was 9.04-10.17 ms^–1. The results of this study suggested the usability of the tested design for the threshing unit in agricultural practice.