An instrument for controlling bleeding includes an outer shaft having a central lumen extending between proximal and distal ends thereof, and an inner shaft disposed within the central lumen of the outer shaft, the inner shaft having a central lumen extending between proximal and distal ends thereof. The rotor has two salient poles which face a respective permanent magnet across a small air gap. After the connection is made, the split ring is expanded through a window in the box connection member and locked in place.