What to measure
Precision bits are small enough that a tenth of a millimetre decides the fit. Measure across two opposite flats of the hex shank with a caliper, on the plain part of the shank and not on the knurled or tapered section near the tip. Most precision sets use a 4 mm hex, and the bits are commonly about 28 mm long, but some watchmaker and older sets use other sizes, so do not assume. Check one bit from each end of your set: in cheap sets the plating thickness varies and a few bits are fatter than the rest.
Clearance, walls and material
The clearance here is 0.2 mm, giving a pocket of 4.2 mm across flats. A small hole prints proportionally tighter than a large one, because the same blob at the seam takes up more of it, so resist the urge to reduce the clearance for small bits. If the bits stick, go to 0.25 or 0.3 mm. The wall between pockets is 2 mm and the wall around them 2.4 mm. Both are thinner than on the quarter inch holder to keep the strip compact, yet they are multiples of a 0.4 mm line, so the slicer fills them with perimeters and leaves no hairline gap in the middle. PLA gives the cleanest small pockets.
Pocket depth
The strip is 10 mm high with a 1.6 mm floor: each pocket is 8.4 mm deep, close to a third of a 28 mm bit. That keeps the bits upright while leaving the tip markings visible. Shallower than 6 mm and thin bits lean and tangle.
Printing
Print flat with the pockets facing up and no supports. Use a finer layer than usual, 0.12 to 0.16 mm, and slow the outer perimeter to about 30 mm per second: the corners of a 4 mm hexagon are tiny, and speed rounds them until the bits no longer enter. Set the seam position to random or to the rear, so twelve seams do not line up on the same pocket corner. If one pocket is tight after printing, turn a bit in it with your fingers a few times to clear it.
Outline drawing
Schematic, not to scale. Pocket centres are 6.2 mm apart.
Parameters the generator will use
| Setting | Link parameter | Value |
|---|---|---|
| Model | model | bit_holder |
| Bits per row | count | 12 |
| Rows | rows | 1 |
| Bit size across flats | across_flats | 4 |
| Pocket clearance | clearance | 0.2 |
| Wall between pockets | gap | 2 |
| Wall around the pockets | margin | 2.4 |
| Strip height | height | 10 |
| Floor under the pockets | floor | 1.6 |
All lengths are in millimetres. Outer size from these values: about 77.2 x 9.6 x 10 mm.
Open the generator with these values
This model needs the $7 licence key: one payment, one key, and it opens all five paid models. Get a licence key on Gumroad ($7)
The hex bit holder strip needs a licence key: without one the generator shows the model locked, lists the values from this link and fills them in as soon as you unlock. The fitted drawer organiser bin is the free model and downloads with no key.