• Long life under continuous slip conditions
  • Unidirectional or bidirectional operation
  • Same or different CW and CCW torques
  • Precise and stable limit torque calibration
  • Range: 1.0 to 600 oz·in
  • Same torque at breakaway as at high slip velocities
  • Slot for pin coupling
  • Corrosion resistant materials
  • Drag torques for supply reels
  • Safe holding of backdriving loads
  • Friction loading of mechanism
  • Friction loads for testing components
Federal supply code - 15531
Unit of Measure


Upper Limit Torque (oz·in)1 N/A 48 ± 5

Unit Weight

N/A 4.1 oz

A (in)

N/A 1.25

B (in)

N/A .2300

C + .0010 (in)

N/A .3125

D (in)

N/A .94

E (in)

N/A .10

F (in)

N/A .61


N/A #6-32

H (in)

N/A .50

J Max. (in)

N/A .68

K - .0010 (in)

N/A .125

L (in)

N/A 1.25

Additional Information

CO-B series drag brakes are designed for long life under continuous slip conditions. The useful life of these elements is a function of transmitted torque and slip speed. The service life factors are based on continuous duty testing on mildly hard wear surfaces. Service life may be extended by a factor of approximately 4X by specifying Nitride surface treatment in "wear critical" applications.

All brakes of this type have a slot for engagement by a pin which prevents rotation by the stationary member. Dimension "F" indicates the recommended radial distance from the axis of the brake to the center of the pin. The axial penetration of the pin in the slot should provide for approximately .010" clearance to prevent bottoming.

Brake arrangement for preventing load backdriving

The raising of a weight quite often causes the problem of load backdriving. This problem is typically noticeable in an efficient transmission when power to the prime mover is interrupted, and the weight accelerates downward driving the transmission and prime mover backward. The brake arrangement illustrated permits the weight and prevents backdriving when power is interrupted.

A bidirectional brake with low drag torque in one direction and high drag torque in the other is a key element in this transmission. When the load is raised the brake exerts a light drag torque, in order to avoid an appreciable increase in motor power requirements. When the load is lowered the brake exerts a high drag torque which is somewhat in excess of the equivalent gravity pull on the weight. This brake torque prevents the weight from backdriving the transmission and motor when power is interrupted.

  • 1 Stock units are calibrated with equal CW and CCW slip torques corresponding to the value of the Upper Limit Torques listed in the table above. Brakes can also be calibrated with slip torque values lower than the maximum values shown. When ordering, the CW and CCW slip torque values may be specified anywhere from the full torque value listed, to a lower value of approximately 1/8 of this maximum, and may be be specified the same or different for each of the two directions of rotation.