Naming:

sd-holder = screwdriver-holder

7X             = 7 slots for screwdrivers

Recommended sizes:

7X  = 4-5 Screwdrivers

9X  = 5-7 Screwdrivers

11X = 6-9 Screwdrivers

13X = 8-11 Screwdrivers

15X = 10-13 Screwdrivers

This is only a recommendation !!!

Lengths:

7X  = 114mm

9X  = 142mm

11X = 170mm

13X = 198mm

15X = 226mm