Read up on the setup and requirement for the slip/ friction clutch for your attachment. But in general it replaces the shear bolt. If its not rusted together and the springs are adjusted correctly the two disc will slip when you get the brush hog in a bind. Usually one would loosen the bolts / springs up quite a bit and make the disc slip. Then tighten back to the correct torque for your setup. Not every one prefers them over a shear pin but I for one am a big fan. No more stoping work and dealing with the frustrating, hot, dusty, tinkering on getting everything lined up to replace the broken shear pins.