Could also connect a bunch of locks and put all the keys on a key ring. Lots of pictures of latch, lock, etc ideas for montessori type preschool. This lock one could be made with 2 boards, some o-rings, and some locks from Dollar Store.
Hooking together caribiners. Clipping carabiners: a great way to improve dexterity while working on a Practical Life task that's inexpensive to put together. As skills grow, you can switch out the activity to screw carabiners.