One of the tools I carry with me almost every day is a precision 4mm bit driver, and various driver bits to go with it. The driver originally came with a holder that attached right to the driver itself, but it eventually broke and I wanted another way to keep my driver bits from escaping, so I designed this.

Prints in three parts, which are then glued together. I couldn't get a consistent grip on the bits just using printed plastic flexures and I didn't want to use magnets for fear that they would pick up ferrous particles over time, so I incorporated slots for rubber o-rings around each bit. I used size 007 Viton o-rings, which have held up great for over five years of my own use.

The holes are deep enough and the o-rings are set high enough that the bits can be stored tip-down, to reduce wear and tear on the inside of your pockets.

Printing: No supports, thin layer height for small details and sharp internal corners (0.15 or smaller).

Assembly: Two 2mm diameter, 34mm-long steel rods are used to align and provide extra structural integrity. but they probably aren't strictly necessary.