Ikea Skadis twinmarker holder/organiser. 

40, 60, 80, 100 & 108 marker versions available (40 and 60 versions are A1 Mini compatible). Minimal support required only for hooks.

The 108 version is a different overall width with a 12x9 arrangement, the rest are 10 slots wide.

Can be a slightly tight fit on some boards due to the large size and the skadis board flexing a bit, better to install first then load with markers to ensure its fully locked in place.