Minecraft wiki entry for Piston, associated text: The piston-only NOT gate, also called an inverter, is slightly larger than a standard redstone NOT gate, so it is rarely used alone. However, it demonstrates an important concept used in many piston mechanisms, namely that torches below solid blocks create a current in any surrounding wire. When an input is triggered, the piston extends, uncovering the torch hole removing the signal from the output line. The input can power the piston from almost any direction. Alternatively, a block of redstone can be used in to shrink the design.