As with the main case itself, there were subtle differences between the Test Set and the Main Release versions; as shown in the images, the main set Tardis lid is hollowed out, giving a lighter and cheaper feel. This is what is believed to be a money-saving method, as the main release produced far more of these than the Test Set, and the cost of the screwed-in inserts imagined it would add up to a substantial amount of plastic and, therefore, costs. The Test Set lid followed the Test Set Tardis case, having a more rigid, premium feel. This can be attributed partly to the similar design to the later released 'Sound FX' version, with an insert screwed in, with space for a padlock.