This kit assembles into a fully functional three-tumbler combination lock. Like a fancy safe lock, when the combination has been entered correctly, an additional turn of the dial past zero engages the bolt and withdraws it, opening the lock.
Because all parts of the lock are made of transparent acrylic, you can see the operation of the code tumblers perfectly clearly. The pins that engage between neighboring tumblers are colored acrylic, so they stand out and demonstrate their function in encoding the combination. By watching from the front, you can figure out the combination. (You can even learn that every combination lock actually has two different combinations: one that works when you start by turning clockwise, and another when you start by turning counter-clockwise.)
And if you want a real challenge, a pair of paper blinds can be inserted to block your view of the mechanism, if you want to try to pick it by feel alone. But be warned, this kind of lock is very hard to pick! (Though some experts are able to do it in minutes.)
This kit goes well with our Pin-Tumbler Lock, and is also available in a set that includes both.