Quantity   Component name
1 × Arduino Nano (or other 328P version) In addition to the Arduino that is running grbl
1 × 4 wires with dupont female connectors on one end Will be 5V, GND, Rx, Tx and connect to the grbl breakout header pins
1 × Rotary encoder and dial/knob You choose. One where the pin order is COMMON, A, B works well with the Arduino Nano's adjacent GND, 2, 3 pins