Base Lab Tools standard metric solid aluminum optical breadboards are 13mm thick and have M6 tapped holes on (2) 25mm grids, offset by 12.5mm in both the horizontal & vertical direction.  Each breadboard has at least 5 counterbore mounting holes which accept M6 cap head mounting screws and a true 12.5mm border so when two breadboards are butted up to each other the 25mm spacing can be maintained.