Really nice feature of the Ernst gripper wrench racks is that they make them in virtually every increment of set size. They come in 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 15 slots in both red and black. The reversed grippers come in 8, 12 and 15 only. I just happened across this recently when I went to their website to explore their entire product line. Certainly nice if you have all the wrench sets you are going to get and want buy one specifically tailored to each set. They also have a 16 slot standard rack and 20 slot graduated rails.
i just ordered 7 slot racks for my Gearwrench Flex Head sets that just have the most commonly used sizes (10, 12, 13, 14, 15, 17, 19mm)
http://www.ernstmfg.com/store/c/51-Standard-Gripper.aspx