Summary

I could noch find any good 8 x 12 grid "Eppi" Tube holder on thingyverse like they are used in a biochemistry / biology laboratory, so I made one.
Distance between the tubes is big enough for the tube caps to stack nicely flush.
Fits 1,5ml and 2ml tubes.
Is stackable thanks to the corners.

Is 18cm wide so it can barely be printed by a Prusa Mini.
Print in PETG for chemical resistance.

Print Settings

Printer Brand:

Prusa

                                            <p class="detail-setting printer"><strong>Printer: </strong>                     <div><p>I3 MK3S</p></div></p>                                                                                <p class="detail-setting rafts"><strong>Rafts: </strong>                     <div><p>No</p></div></p>                                                                                <p class="detail-setting supports"><strong>Supports: </strong>                     <div><p>No</p></div></p>                                                                                <p class="detail-setting resolution"><strong>Resolution: </strong>                     <div><p>0.20</p></div></p>                                                                                <p class="detail-setting infill"><strong>Infill: </strong>                     <div><p>20</p></div></p>                                                    <strong>Filament:</strong> Prusament PETG                clear violett                    <br>                        <p class="detail-setting notes"><strong>Notes: </strong>                    </p><div><p>PETG is resistant to many chemicals / solvents, which is desirable in a laboratory setting.<br>It still can <em>not</em> be autoclaved or dry heat sterilized, as it would melt. </p><p>Don't bother with high infill %, it is an absolute brick even at ~20%, low z-Resolution and simple fast square grid infill, as all the tube holes support the structure against torsion.</p></div>

"Eppi" Tube Rack (1,5 & 2 ml, 8x12 grid)