The frame is 1" wide and was formed using a picture frame bit. A rabbet was cut on the back of the frame to allow for the insertion of the plywood back.
There are four rows of eight keys. Each key is held in place by a loop of wire that pokes through a hole behind each key. The colors of the wires were chosen to blend in as closely as possible with each key. The ends of the wires are secured to the back of the panel with screws.
See also: Item #1.