A Clutch Pack is the stack of alternating friction and steel plates inside a limited-slip differential that resists speed difference between the two output shafts. Alternate plates are splined to the side gear and to the differential case, so any relative rotation between the two must slip the plates against each other, and the resulting friction transfers torque toward the slower wheel. The clamping force comes from a preload, typically from Belleville springs or a spring pack, plus a load-dependent component generated by ramp angles that push the side gears outward in proportion to the torque passing through. Changing the number of plates, their arrangement, the preload and the ramp angles is how a clutch-type differential is tuned for drive and overrun locking, and because the plates wear and depend on the correct friction modifier in the lubricant, the pack requires periodic service.