The wood backing is about 31" x 18.5" and came from a Snap On tool box. However, it would fit in any other similar sized drawer and could also be cut down if needed.
It has (15) different socket rails screwed down to it.
It looks like about (9) of the rails are the original Snap-On rails with the part numbers showing, I didn't see the part numbers on the others.
The clips on the rails include sizes 1/4" 3/8" 1/2" and 3/4"