This is a model of a pin-tumbler lock mechanism in the form of a small lockable box, just big enough to hold a gift card, some money, or a secret message. The components of the kit are made of transparent acrylic to show very clearly how all such locks work: the pins, held in place with springs, block the barrel of the lock from opening. When the key is inserted, the pins all line up exactly with the edge of the tumbler, allowing the gift tray to slide out. If you give this model as a gift, assembled with a card inside, you can decide whether to give the recipient the key (easy to open) or just the included lock pick (for a challenge).
This kit includes 60 parts and took us about thirty minutes to complete. Measures 3-3/8" x 4-3/8" x 5/8" once assembled.