Using a design from an old bike lock, this puzzle helps the user understand series'. Four of the numbers on the wheels make a well known series. The other numbers are chosen so they don't make a series. Once you line up all the numbers in the series the lock comes apart. Younger students may need to be provided the first and possibly the second number in the series. The current set of wheels makes the series 2-4-6-8. Other sets are in progress.Print the parts. Ideally print the base and key on the same plate to avoid them getting too soft (good cooling will help with that too). Low infill is fine. We printed ours at 75% size, but it should work all the way down to 50% if you want smaller ones that print quicker. 100% size is nice and large for younger kids. The prints are designed to print fine without support. Assemble by putting the wheels on the base (be careful with the order and orientation). Secure the wheels by super gluing on the clip to the end of the base. Slide the key in and spin the dials so it is ready for the kiddos. You'll notice the base STL is a bit thicker than pictures. After assembly we noticed a thicker base would make it easier to kids to hold onto it without accidentally griping the wheels. In progress, but not done before the deadline: