This image shows the Morse-Vail straight key, the most influential early telegraph design. It has ten essential parts: the knob, lever, frame, and base form the physical structure. The upper and lower contacts—hammer and anvil—complete the circuit when pressed. A spring and two screws adjust contact gap and lever tension. The trunnion screws let the lever pivot, while a return spring resets it. Later models added a shorting switch to reduce noise when idle.
Each press sends a pulse—dot or dash—in Morse code. Invented by Morse in 1837, this key replaced his earlier portarule design. Alfred Vail’s refinements made it practical, robust, and easy to use, launching the telegraph era.