The invention provides a cartridge-mounted mechanical seal in which a set of bellows acts against the rotary component to urge its face into mating contact with the stationary component face, and wherein the stationary component is mounted in the seal so as to allow it a degree of pivotal movement, in use, relative to the stationary parts of an item of equipment in which the seal is used, about an axis perpendicular to the longitudinal axis of the seal, hence maintaining the stationary and rotary components substantially in alignment despite any out-of-squareness in the equipment. The invention also provides a self-aligning stationary unit which might be used in such a seal, in which unit a stationary seal face is pivotally mounted about one or more primary pivot pins set in a pivot ring, the pivot ring in turn being pivotally mounted about one or more secondary pivot pins set in a gland plate which, in use of a seal incorporating the unit in an item of equipment, will remain fixed in position relative to stationary parts of the equipment, the primary pivot pins being located in slots provided in the stationary seal face.