The shallowest under-mount drawer guide that Blum makes is a 9" slide, the shallowest cabinet that a 9" drawer guide will fit into is a 294mm (11-1/2"). In KCD, we will not allow you to make any cabinet that has a drawer in it less then 294mm (11-1/2") deep.
For cabinet depths from 294mm (11-1/2") to 355mm (14") we will machine for a 9" under-mount drawer guide, and the drawer box depth will be 9".
For cabinet depths from 356mm (14-1/16") to 431mm (17") we will machine for a 12" under-mount drawer guide, and the drawer box depth will be 12".
For cabinet depths from 432mm (17-1/16") to 507mm (20") we will machine for a 15" under-mount drawer guide, and the drawer box depth will be 15".
For cabinet depths from 508mm (20-1/16") to 584mm (23") we will machine for a 18" under-mount drawer guide, and the drawer box depth will be 18".
For cabinet depths from 585mm (23-1/16") to 661mm (26") we will machine for a 21" under-mount drawer guide, and the drawer box depth will be 21".
For cabinet depths from 662mm (26-1/16") and deeper, we will machine for a 24" under-mount drawer guide, and the drawer box depth will be 24".