1. Four weeks of the board with four screws holes hole diameter 3mm easy to install and fixed 2. Relay made of high quality loose music relays. A common terminal a normally open one normally closed terminal 3. Optocoupler isolation good anti-jamming 4. Low pull high release. Energisation status indicator lights D1 D1 status lights off when you release 5. VCC of system power JD_VCC relay power. Default hair 5V relay you can plug in jumpers 6. Relay Maximum output: DC 28V/10A AC 240V/10A Wiring: VCC: positive power supply system GND: System power negative IN1: relay control ports A product for Arduino that works with official Arduino boards.