Stuffing box

A stuffing box is the gland that seals around a shaft where it passes through a bulkhead or the hull, packed with rings of soft material compressed by a follower to grip the shaft and hold back water or oil. The aft engine-room bulkhead shaft gland and older water-lubricated stern seals use braided packing rings tightened just enough to seal while letting a slight drip cool and lubricate the packing. Over-tightening burns the packing and scores the shaft; under-tightening floods the space. Modern oil-lubricated stern tubes replace the packing with lip-seal or radial face-seal cartridges, but stuffing boxes survive on rudder stocks, valve spindles, and pump shafts.