Minecraft wiki entry for Clock, associated text: A 10 Hz clock runs too fast for some redstone components to respond to. Command blocks and note blocks can handle the rapid activation. Doors, trapdoors, and fence gates produce sounds as if being activated and deactivated that quickly, but appear and act as if constantly activated. Pistons act as if constantly activated, but the 0-tick off-pulses produce the flickering appearance of a deactivated piston overlapping the activated piston. Other redstone components simply act as if constantly powered.