The 6C-DE-104/16-3.75S board allows two stacks of PC/104 boards to be joined with the solder side of both stacks facing the 6C-DE-104/16-3.75S board. An alternate is to use the 6C-DE-104/16-3.75P board and have the component side of each stack facing the 6C-DE-104/16-3.75P board.
Options:
*6C-DE-104/16-3.75-S
6C-DE-104/16-3.75-P