This is rack to hold 10 test tubes. Mine measured 19.8mm outer diameter, 20mm would probably fit as well.

Fusion360 source file is included so you can tinker around with it if you like. There is a user parameter for tube diameter so it should be easily adjustable to other tube sizes. I recommend setting this parameter about 0.5-1.0mm larger than actually measured so they don't get stuck in the rack.

Print instructions

Category: Organization Print Settings

Printer Brand: Prusa

Printer: i3 MK3

Rafts: No

Supports: No

Resolution: 200um

Infill: 20%