Features: brand new and high quality Supports A+/B+/2B/3B/3B+. High quality relays, loads up to 5A 250V AC or 5A 30V DC. Photo coupling isolation, prevent interference from high voltage circuit. Standard rail mount bottom case. Onboard LEDs for indicating relays status. Relay control pin selection jumper, allows to control the relays by custom pins other than the default pins. Reserved control Interface, allows to work with controllers like PLC. Comes with development resources, including examples in wiringPi, bcm2835, python, python-bottle (webpage control), and crontab (cron job). Specifications: Power supply voltage: 5V Trigger signal: 3.3V/5V Relay channels: 8-ch Contact form: SPDT-NO,NC Closed current: 6mA (per channel) Connector: screw terminal block Dimension: 232x72 (mm) Mounting hole size: 3.0mm Package Includes: 1 x 8 channel relay extenstion board 1 x Rail mount bottom case 1 x Screws set ( not include Pi) note: Due to the problems of lighting effects and shooting angles, there will be certain tolerances in the product, please understand. Please allow 0-1cm error due to the manual measurment.