I wanted to customize my Wiha toolkit (the "Wiha 75965 65 Piece System 4 ESD Safe Master Technician Ratchet and MicroBit") to have room for ¼" bits, a larger socket set, and additional tools. This insert has space for 30 x 4mm bits, 24 x ¼" bits, and 12 x ¼" drive sockets, while taking up only about half of the box. I'm using the other half to hold 4mm and ¼" drivers, a Wiha ratchet, tweezers, pliers, a ruler, and driver extensions. 

Printed in TPU. I had a heck of a time not getting stringing, so to prevent the stringing from clogging up the bit holes I selected the “Avoid crossing perimeters” setting which helped. I also made a modifier region around the socket storage area for 0% infill, but that may have been unnecessary.