I made this case to replace the broken case the bits came in. Kinchrome Hex & Spline Drive Set 23 piece. The large bits are 10mm. Added the ¼" bits from other old sets to fill up the gaps. The filler stops the small bits coming loose. I used ABS and glued the handles using acetone. I used the excellent thread.scad include from here https://dkprojects.net/openscad-threads/.