Sargent & Greenleaf, Rochester, New York - 4 movements, Model K
By the 1890's the time lock industry had reaped enormous benefits from the time lock's broad commercial adoption, the advent of modular movements, and a general expansion in the banking industry. These factors had lead to time lock mechanisms that were exceptionally reliable and quite user-friendly- rare lockouts stemmed from user error, such as setting the time lock with only one operational movement. Concurrently, the architecture of the banking industry, of both buildings and the vaults they housed, had become symbols projecting stability, wealth and power. These changes in banking led to a sharp growth in the number of extremely large vaults at the end of the nineteenth century. While not technically impenetrable, these vaults represented such great investment - and such staggering expense should they need to be forced open - that they required a time lock whose release was all but certain.
In response, Sargent & Greenleaf introduced their Model O for conventional manually bolt work concurrently with their Model K to operate with automatic bolt work in 1893. Aside from its four 72 hour 'L' sized movements (identified by their curved, bottom bottom-positioned indicator arrow and partial front front plate that leaves the escapement clearly visible from the front), the Model K and O was fashioned much as an extension of other Sargent designs, with a jeweled bronze case (later as with all their other models moving to satin silver and in some cases satin bronze cases finishes), nickel-plated low-profile bolt, bottom mounted snubber bar, square door glass, and the simple handcuff-type door lock now standard on Sargent's time locks.
The marginal benefits of a fourth movement represented reasonable expense to only a small subset of the time lock market. One subjective benefit was the conspicuous investment in security - a large time lock proportional to a large vault door was synonymous with financial wherewithal. In other words a marketing tool. However, rather than the certainty of unlocking, the major benefit of the four-movement time lock was the assurance of regular operation, uninterrupted by maintenance or repair.. Even with a malfunctioning movement the Model K or O offered the industry-standard dependability of a three-movement time lock, allowing for confident use and a relaxed appointment for service or repair.
Due to the general rarity of of the largest vaults, the Model K and O was scarce even in its own day fewer than 300 of each model are thought to have been made. Sargent would go on to offer other four-movement models and other makers would design their own, yet the total market for this type of supreme security would always be small, making all four-movement time locks uncommon. Furthermore, the high profile that four-movement time locks operated under meant that almost every one was used extensively and maintained and repaired diligently, making any four-movement time lock with consecutively numbered movements exceptional. (1)
A. Model K, (later model #6404). c. 1893-1895. The Model K was introduced at the same time as the Model O and uses same sized movements designated as 'L' as in their Model O, but has no drop bolt. Equipped with a trigger at the bottom of the case that would be used to actuate an external bolt motor device. Notice the Gothic font style of the etched logo - a rarely seen style. Case stamped #3, consecutively number movements #2969, #2970, #2971 and #2972. file 109
(1) American Genius Nineteenth Century Bank Locks and Time Locks, David Erroll & John Erroll, pp. 272-274