The prototype's enclosure was made out of waterjet acrylic. That proved to problematic for several reasons. This is a 3D printed version with an improved component layout that better separates the temperature sensor from the gas sensor's heater for more accurate measurements. The nuts and bolts are M3. For the Yun use 8mm threaded standoffs, for the MQ-2 use a 16mm length. McMaster-Carr is a good source for such things. https://github.com/ductsoup/Air-Quality-Sensor-Suite