There are two rounded corner versions of the tilted LCD cover here. One is for the laser cut acrylic front plates and has tighter tolerances for the 1/8" nominal thickness acrylic. The other (marked with a M-3D) is for the machined aluminum front plate or for the 3D printed front plates found here: http://www.thingiverse.com/thing:2096308

Even though they look similar they are not interchangeable. The one will be too tight and the other too loose if mounted on the wrong version of the front plate.

Align the left side first when attaching to a face plate and then pop the right side in by gently pressing the locking tab in to secure it to the mounting hole. The fits will be very snug.

As these are precision fit parts it is highly recommended that you use calibrated filament using the system found here: http://www.thingiverse.com/thing:1037301