The case was designed to fit a small NodeMCU Esp8266 Board. It has some spare space for sensors or cables and has ventilation holes. The Board needs to be inserted upside down, so that the pins are reachable. I glued mine in to ensure extra stability while plugging in the micro USB plug. I have 3 prints in use, two with ds18b20 sensors and one with a 433Mhz transmitter and everything fits perfect.