This is a case for the macpod mini-mill tachometer v2 which can be seen at http://macpod.net/misc/sx2_tachometer/sx2_tachometer.php .
It attaches to the mini-mill on the back top of the control box with double-sided tape, as shown in the last picture. I also used double-sided tape to hold the circuit board inside the case on the led side, which isn't shown. The cables enter the control box thru the original tachometer socket which I removed. The case screws are 2-56 machine screws.
I printed it with PLA, use your usual settings, nothing special.