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.