The sixth and seventh series continued to introduce action-packed storylines and new characters, and saw the introduction of a writing staff. The sixth series in 2002 was an attempt to create a spin-off based on the successful "Bob the Builder" series. Two episodes introduced a group of construction machine characters known as "The Pack". The spin-off did not materialise for some time. Eventually, in 2006, thirteen episodes were released straight to DVD in two collections: "On Site with Thomas" and "Thomas' Trusty Friends". It was the first series broadcast on ITV since series 3.