This module has size of 75mm in length and 55mm in width 19.3mm in height.The board with four screw holes, hole diameter 3.1mm, easy to install and fix.Relay selection of quality loose music relays, SPDT. A common terminal, a normally open, one normally closed terminal.Low pull, high release. Energisation status indicator light, release status LED is off. VCC stands for the system power, JD VCC for the relay power. It support all MCU control,the industrial sector,smart home control etc.