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A New Kind of Lock
In 1913 Emil Christoph applied for a patent for his new lock. At the time it was called a plate lock, but is better known today as a wafer lock. The wafer lock had actually been invented a half century earlier, but, like the pin-tumbler lock, required extensive machining to produce, and so was lightly regarded.

Christoph's lock used a double-sided key. Christoph envisioned an almost unlimited number of change keys, based on minute changes of the tumblers, although this actually proved to be impractible.

A New Manufacturing Process
One of the reasons that the use of wafer locks skyrocketed was because they could be made much less expensively than pin-tumbler locks. Using the relatively new process of die-casting, the lock itself could be produced at an amazing rate, and the product required little, if any, additional hand finishing. Simplifying the matter even more, the wafers themselves could be stamped out of sheet metal, as could the keys.

A New Market
Wafer locks in the late 1800s were almost as expensive to manufacture as pin-tumbler locks. Worse yet, they competed directly with pin-tumbler locks in the marketplace, for use as door locks, cabinet locks, desk locks, and so on.

By 1915 the automobile industry was wide open and people began demanding better locks for their cars. All of these factors combined to allow the success of the wafer lock.

Double-Sided Wafer Locks for Antique Cars

Better Security for the Masses

switch with king lock
Early Briggs & Stratton switch with King lock
plug and key for king lock
The lock plug from the switch at left. The pair of scratch marks across the wafers were probably from the factory.
wafers for king lock
Three different materials were used for the wafers, each being of a different thickness, probably to control end play.
king lock with briggs switch
The keys for this ignition switch are marked Basco
king briggs plug
This later version contains twenty wafers of uniform thickness. There are no springs in this lock or the one above.
Besides the use of wafers in their new lock design, King locks departed from another industry standard. Pin-tumbler locks were designed with separate, distinct, and equally spaced cuts so that with the key inserted, the pins rested at the bottom of the cuts; because the King double-sided key used a gradual undulating curve and the wafers were presented as a "pack", each individual wafer could come to rest at a low spot, a high spot, or somewhere in between. Lock design for double-sided wafer locks eventually diverted, with some maintaining the undulating keys and associated wafer packs while others used discrete depths and spaces for their keys such as used with pin-tumbler locks.
Briggs & Stratton switches as above were the first to use the new wafer lock as early as 1915 for Chevrolet. When Ford began using them for the electric start Model T in 1919, the locks used distinct depths and spaces.  

Clum Manufacturing was another early provider of double-bitted wafer locks. The cross section of the Clum key looks very much like that of the King key. An outstanding feature of the Clum key is the patent date shown on the reverse, August 15, 1916. While a Clum patent of that date exists, examination of the patent contains no mention of either the key or the associated lock. There was a patent submitted later that year that discussed the lock, but not actually issued until years later.

clum reverse with patent