The Permutation Lock: Tumbler Wheels You Can Re-set

"This invention relates to an improvement in that class of locks in which the tumblers are formed by encircling an inner ring or wheel with an elastic stop-ring, which is generally held in position by its friction upon the inner ring". Brettell forms the stop-ring "to give it a bearing at three points within a groove which encircles the inner ring, at two of which points, namely, those nearest the opening in the stop-ring, a series of triangular teeth are formed which lock into corresponding teeth formed in the bottom of the groove". "In order to set the stop-ring at any desired point upon the ring A, a key of proper form is forced into the opening c in the stop-ring, thus spreading it sufficiently to raise the teeth a a' out of the serrations in the groove of the ring A, when the latter may be turned so as to bring any desired part of its periphery opposite the opening in the ring B." He does not claim merely roughened rings: that "only increases the friction of one part upon the others, but does not securely lock them together until released by spreading the outer ring".

Cut two plywood discs 80 mm across and one 40 mm drive disc. Cut a gate, a notch 8 mm wide, in each large disc's rim. Glue a short dowel pin to the front face of the drive disc and to the front face of the first wheel, near the rim, so each can catch the next wheel's pin. Stack them loosely on one bolt through a base board: drive disc, wheel one, wheel two. Mark 0-39 round the drive disc. Fix a strip of wood above the stack as the fence: it can drop only when both gates are under it. Turn the dial two full turns one way to gather both wheels, then to the first number; one turn the other way past it, then to the second. Watch the pins pick the wheels up. Move one gate by re-gluing its pin elsewhere: that is what Brettell's key and stop-ring do without glue.

**Edward W. Brettell** of New Haven, Connecticut, filed US 145,618 on 3 May 1873; it is dated 16 December 1873. The patent covers the tumbler only, not a whole lock. **Honest limits.** The patent does not describe the dial, fence or bolt; the notebook's lock is the general wheel-pack principle. Dial size, wheel count, gate width and time per try are examples.