Flat hop-up rubber Prometheus. Possible to combine with the proper Flat tensioner by Prometheus.
What is flat hop-up?
Difference between hop-up and flat-up system is in rubber and nob. In the flat-up system rubber doesnt have protrusion and the nob is longer. With this system the bullet has bigger rotation and accuracy. Heavier BBs than normal should be used for proper functioning of the flat system (due to higher rotation of the BB).