This depends on which type of door and lock/latch you choose.
Lever lock handles are used in conjunction with a 5 lever mortice lock, usually on exterior doors that require locking (i.e. front/back doors).
Lever latch handles are used in conjunction with mortice latches, usually on interior doors which don’t require locking (i.e. living room doors).
Lever bathroom sets are used in conjunction with a bathroom mortice lock which can be locked via a thumbturn on the inside and opened from the outside with a coin during an emergency (e.g. bathroom doors).
Lever Euro handles are used in conjunction with Euro cylinders and Euro sash locks, usually on exterior doors (e.g. patio/conservatory doors).
Espagnolette lever handles are used in conjunction with multi point locks and Euro cylinders on sliding/bi-folding door sets and modern front doors which use these locking systems.
All lever handles have a measurement called the “centre” which refers to the distance between the centre of the door handle and the centre of the keyhole. This distance dictates which type of lock is needed. All our lever handles have standard centre measurements to fit all standard British locks/latches.