Btw, on a small clarification. The barrel and curtain were invented first half of 19C but not combined until after Hobbs's picking exploits in Britain 1851, as far as can be ascertained. Combined, they are much more effective. British lever locks mostly use keys with round stems, so they rotate easily.
Flat keys do not, so that cylindrical piece is provided, and is properly called a trunnion. It might, or might not, include a bolt thrower. If so, that allows a small key to achieve a longer bolt throw. It also prevents a worn key from short-locking.
Flat lever keys are now uncommon, tho in Britain many such locker locks are used. There are also safe deposit locks.
Late 19 - early 20C both Yale and S&G made such door locks commonly for residential and business use, but they lost market share to the pin tumbler lock.
Here is the FA sheet for a modern prison lock
http://www.southernfolger.com/files/Fol ... l_Lock.pdf
