Lever tumbler lock (English Wikipedia)

Bellis, Mary (8 November 2011). "The History of Locks". About.com Inventors. About.com. Archived from the original on 30 May 2012. Retrieved 8 November 2011.

archive.today

Bellis, Mary (8 November 2011). "The History of Locks". About.com Inventors. About.com. Archived from the original on 30 May 2012. Retrieved 8 November 2011.

Priess, Peter J. (26 September 1979). A Study of Surface-Mounted Door Locks from a Number of Archeological Sites in Canada. National Historic Parks & Sites. ISBN 9780660101804 – via Google Books.
Price, George (1856). "A Treatise on Fire and Thief-proof Depositories, and Locks and Keys". Simpkin, Marshall and Company – via Google Books.
Friend, Mick (2004). The Encyclopaedia for Locksmiths. Authors On Line Ltd. ISBN 9780755201174 – via Google Books.
Pulford, Graham (17 October 2007). High-Security Mechanical Locks: An Encyclopedic Reference. Butterworth-Heinemann. ISBN 9780080555867 – via Google Books.
Tobias, Marc Weber (1 January 2000). LOCKS, SAFES, AND SECURITY: An International Police Reference Two Volumes (2nd Ed.). Charles C Thomas Publisher. ISBN 9780398083304 – via Google Books.

"Lockshop Warehouse". 2 & 3 lever mortice locks are generally only recommended for use on internal doors as they do not provide adequate levels of security externally