This dry erase marker holder was designed to clip to my glass boards hung on my wall. The glass is .150" thick and the clip has more than adequate clamping force for four markers. Build the part vertically for best results. Place markers in the holder upside-down to keep the tips from drying out. 

 If you have two spools of the same material or don't care if this is two colors, I'd recommend splitting the clip portion into a seperate part and merging the clip and marker tray in cura so you can use solid infill on the clip and low density infill on the rest of the part. It'll speed up printing quite a bit and you'll get the same mechanical integrity as before.