The FOPB-N electromagnetic mag-particle brake series provides a fast response. Over-excitation circuits quicken the response rates further. The torque is independent of speed and at the same time, proportional to the voltage applied to the field. The OP units are sealed to prevent wear particles from contaminating the machine. This also avoids contamination of the clutch by the machine environment. The sturdy construction of the OP series unit and the precise formulation of the magnetic particles combine to provide it an extended life. The unit is to be mounted horizontally. If the unit is used in a slanted or vertical position, torque will not be consistent.