In the past complex tools were often known as engines. Clock-barrel engines were used for cutting the spiral groove to take the gut lines of an eight-day long case clock barrel. The tool was made rather like a pair of turns in which the barrel to be cut was centered, on its winding arbor, between a runner and a rotating or driving arbor. This arbor, which held the barrel winding square, was threaded along its length on which a block or carrier would travel axially as the work was turned. An arm extending from this block carried the hand cutter, and as the barrel was turned towards the operator pressure was applied to the cutter to form the spiral groove in the barrel.