A lever tumbler lock is a type of lock

Lock (device)

A lock is a mechanical or electronic fastening device that is released by a physical object or secret information , or combination of more than one of these....

 that uses a set of levers to prevent the bolt from moving in the lock. In the simplest of these, lifting the tumbler above a certain height will allow the bolt to slide past. The number of levers may vary, but is usually an odd number for a lock that can be opened from each side of the door in order to provide symmetry. A minimum number of levers may be specified to provide an anticipated level of security (see 5 lever lock

5 Lever Lock

The 5 lever lock is a type of lock often required for home insurance and often recommended by the police for home security. There are various grades but the current British Standard is usually required for insurance purposes...

).

'Double acting' lever tumbler locks were invented in 1778 by Robert Barron

Robert Barron (locksmith)

Robert Barron was an English locksmith notable for his invention of the double–acting tumbler lock in 1778.-References:...

 of England. These required the lever to be lifted to a certain height by having a slot cut in the lever, so lifting the lever too far was as bad as not lifting the lever far enough. This type of lock is still currently used today.

Lever locks generally use a bitted key

Bitting

A bitting is the part of the key that actually engages the tumblers to activate the lock. Bittings are often represented as a code which instructs how a key is to be cut by a locksmith. The bitting is usually a series of integers that is usually translated from a key code chart or from a...

. Some locks used on safes use a double-bitted key, as do some door locks of a type often used in Southern and Eastern Europe.