A double cone shape drum device was developed, and inserted in the construction of the Turkish threshing machine in order to increase the machine threshing efficiency and capacity, and to improve the threshed grain quality. The wheat threshing by the investigated machine before and after development was tested, compared, and evaluated versus different drum speeds and grain moisture content levels. The comparison, and evaluation based on the threshing efficiency related to the percent of un-threshed grain; the grain quality related to the percent of damaged grain; and the machine threshing capacity related to the drum speeds. The results showed that the wheat threshing efficiency was ranged from 96.8 to 99.3%), % for the developed thresher, while it was nearly from 92.6 to 97.25% for the Turkish thresher before development. The results also indicated a marked improvement in the final grain quality for the thresher equipped with the developed drum (95.88%) compared to the thresher before development (93.13%). In general replacing the developed drum device  instead of the traditional one in the construction of the Turkish threshing machine led to increase the machine capacity by about 12.6 % ,and was very competitive.