Coupler Cap + Adaptor for Ultimate Filament Drybox

UPDATE April 24, 2026:  I have published the third generation of my Coupler Cap for Cereal Container Drybox as Filament-Holding Drybox Cap.  The new Gen 3 version grips the filament very firmly, and it has much smoother operation than earlier versions!  I recommend using the new version, but if you still want to use this version...

This Coupler Cap for the Ultimate Filament Drybox is a thorough redesign of the Coupler Cap from @GunplaMark's The Ultimate Cereal Container Filament Drybox that improves the grip on the filament and eliminates the bending of the end of the filament as seen with the original design.

Simply push the end of the filament all the way into the Coupler Cap, and the internal gripper holds onto the filament; then press the Coupler Cap onto the coupler on the drybox.  The filament will wind back onto the spool to help prevent tangling if you're using my Auto-Rewinder for Ultimate Filament Drybox.

The Coupler Cover is a new part (not a remix) that can be used to seal a coupler opening when:

1 - There is no filament in the drybox and you want to seal the container to preserve desiccant within the drybox

2 - You don't plan on using the filament for a while and want to simply store filament in the drybox with desiccant

3 - You have more than one coupler on the drybox to allow feeding filament from multiple locations (such as top plus side exits) and want to seal the unused opening

As of December 4, 2025, I've added an Adaptor to allow this Cap or Cover to be stored on Mark's extended system front piece!  Simply push the adaptor on to the front piece until it is fully seated (please refer to photos), and you'll be able to store your Cap when it's not covering the filament exit coupling.  This Adaptor must be printed with painted-on supports as provided in the 3MF file for proper fit.

Both the Coupler Cap and the Coupler Cover would ideally be printed in TPU (Flex) 95A filament, although PETG will work fine if you don't have TPU.

IMPORTANT NOTE:  this Coupler Cap has a round outer shape, so it does not work with Mark's original Tag Holder - which clips onto the original Coupler Cap; instead, use my Improved Tag Holder for Ultimate Filament Drybox - which remains on the drybox at all times - the filament tag only needs to be swapped out when a different brand or color of filament is loaded into the drybox.

The following photo shows the Coupler Cap holding onto filament as it's being pulled into the drybox by my Auto-Rewinder for Ultimate Filament Drybox:

The following photo shows the Coupler Cap holding filament and sealing the drybox:

The following photo shows one Coupler Cover (no filament in drybox) and three Coupler Caps (holding filament) in use:

The following render shows a Coupler Cap with cutaway views to show the internal structure:

The following render shows a Coupler Cover with cutaway views to show the internal structure:

The following render shows Mark's original Coupler Cap design next to my new Coupler Cap design with cutaway views to show the internal structure:

The following photos show the new Adaptor that allows you to store your Cap or Cover:

To allow modifications, I have provided STEP (.stp) files for the Cap and Cover and an STL (.stl) file for the Adaptor.

PrusaSlicer 3MF files have been provided for all parts.

The Coupler Caps and Coupler Covers seen in the photos were printed with Transparent Giantarm (95A) TPU with a 0.4mm nozzle at 0.2mm layer height with a 15% honeycomb infill and concentric top and bottom fill pattern.  Supports are not needed.

The Adaptor seen in the photos was printed with White Sunlu PETG with a 0.4mm nozzle at 0.2mm layer height with a 15% grid infill and painted-on supports.

Be sure to check out my other designs - including universal key covers and a diverse collection of household accessories and 3D printing tools - on Printables at https://www.printables.com/@PhilCaruso/models