Abstract: The invention provides a three-dimensional puzzle consisting of a plurality of interlocking components. Each component has at least one engagement surface with which it engages with one or more other components. The puzzle includes at least three components in which the first and second components engage and the third component engages both first and second components and prevents their disengagement from each other whilst engaged with the third component. Further, there is provided a device for hot wire cutting of thermoplastic material comprising an electrically conductive wire, an arrangement for driving the wire between two points, and a voltage arrangement for applying a potential difference to the wire between the two points.