DMM Clock -- Mask
The middle piece is the main support for the LEDs -- they're pushed into those holes. The lower piece goes on top and accomodates the rounded tips of the LEDs which are a little longer than the support piece is thick.
At the top is a cutting guide (written in PostScript, of course!) glued onto a piece of foil. This goes on top and makes tiny square windows for the LEDs to shine through. Two widows per LED (per segment) as a homage to the original LEDkit clock.