Each tumbler step of a large Chubb key can be given one of thirty different heights; the bolt step one of twenty. By merely transposing the order of the steps in a six-step key it is possible to get 720 different combinations. By diminishing or increasing the heights the possible combinations may be raised to the enormous total of 7,776,000!
THE YALE LOCK,
which comes from America, works on a quite different system. Its most noticeable feature is that it permits the use of a very small key, though the number of