 Generally there is either no dial present in a skeleton clock, the dial is clear, or it has been limited to a ring around the edge of the case to provide a mounting surface for the hour markers.In the case of skeleton wristwatches, the back will usually be made of sapphire crystal or another clear material that affords easy examination of the parts protected within both from the front and from behind.In addition, several authors have published construction manuals on skeleton clocks in clockmaking and model engineering journals in the UK and USA, several of which (UK) have ceased operations.