This is a 3d model of an Altus Metrum EasyMini rocket altimeter. I wanted to know if an EasyMini would fit in a 29mm min-diameter high power rocket I'm making before I spent the money to buy one. So, I used the measurements and photos from their website to make a 3d model. It looked like it would work, so I bought one and then updated the model. This version isn't perfect, but it's really close to the size of the EasyMini (version 1.0).
There are 3 model files included. For most printers, you'll want to print the "top" and "bottom" files then glue them together. The full model file is also included in case you'd like to use that to model other parts (i.e. your rocket's avionics sled). Once you print the top & bottom, glue them together using a plastic glue. For orientation of the two halves, refer to Altus Metrum's website.
For your reference, the circuit board itself is about 1.6mm thick. The EasyMini's overall height is about 12.5mm, width is 21mm (plus a very small amount for the USB connector) and the length is about 38.7mm.