The only material where the spring will actually work as a spring is White Strong and flexible.
DO NOT ORDER IN ANY OTHER MATERIAL IF YOU WANT THE SPRING TO FUNCTION.
Assembly is pretty self explanatory, however it is important to point out the spring slides over the key handle shaft from the top (where the handle connects to) so that the spring locks onto the key shaft. If you place the spring on from the other side the key handle shaft will not be long enough to fit down in to the hole at the bottom of the body.
Glue the gears onto the shafts only after using a pencil to mark the proper locations. The 4 protruding pins on the bottom of the spring, get glued to the connector on the top of the body.