Coupler Cap Gen 2 with TPU Filament Clutch

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 Second generation of my improved Coupler Cap for the Ultimate Filament Drybox is a 2-part design consisting of a flexible TPU Base and a PLA or PETG Knob that snaps on to the TPU Base and is twisted to engage a clutch that firmly grasps the end of your filament before you slide the Coupler Cap onto the PC4-M10 coupler on your drybox.

This Coupler Cap Gen 2 is a perfect companion to any drybox with a filament spool rewinding system - such as my Auto-Rewinder for Ultimate Filament Drybox - holding on to the filament so it doesn't get pulled into your drybox when it's not being used for printing AND then sliding on to the PC4-M10 coupler to seal the opening.

This Coupler Cap Gen 2 replaces the Coupler Cap from my original Coupler Cap + Adaptor for Ultimate Filament Drybox. Refer to that project if you're looking for the Coupler Cover or the Adaptor for Mark's Extended System Front Coupler Cap Holder.

Note that this design has only been tested with Shore 95A TPU - harder or softer TPU may not work properly!

This Coupler Cap Gen 2 consists of two parts that are snapped together after printing:

1 - Base - printed in flexible TPU (ideally Shore 95A)

2 - Knob - printed in PLA or PETG (or any other hard filament type)

The following illustration shows the process for assembling a Coupler Cap Gen 2:

To use the Coupler Cap Gen 2:

1 - twist the Knob on the Coupler Cap so that the raised bumps on the side of the Knob are about halfway between the raised bumps on the Base (to release filament clutch)

2 - push the loose end of the filament all the way into the Coupler Cap

3 - twist the Knob on the Coupler Cap so that the raised bumps on the side of the Knob are aligned with the raised bumps on the Base (to engage filament clutch); if the turning motion feels unusually tight, just twist the Knob in the opposite direction this time; the TPU clutch fingers are flexible, and switching direction should straighten them out if they get bunched up

4 - push the Coupler Cap Gen 2 onto the PC4-M10 coupler on the drybox; a raised lip inside the Base helps to seal the Coupler Cap on the coupler and may give some resistance as it slides on the coupler; just keep pushing - as an air pocket inside the Base will compress to accommodate the coupler

Once you get used to using these Coupler Caps, you'll see it just takes a couple of seconds to use them!

The following illustration shows the process for securing filament with the Coupler Cap Gen 2:

To remove the Coupler Cap Gen 2:

1 - pull the Coupler Cap Gen 2 off of the PC4-M10 coupler; a raised lip inside the Base helps to seal the Coupler Cap on the coupler and may give some resistance as it slides off the coupler; just keep pulling

2 - while holding on to the filament, twist the Knob on the Coupler Cap so that the raised bumps on the side of the Knob are about halfway between the raised bumps on the Base (to release filament clutch)

3 - pull the filament out of the Coupler Cap

4 - load the filament into your printer (or otherwise secure the filament)

The following photo shows a Coupler Cap Gen 2 holding filament:

The following photo shows a Coupler Cap Gen 2 holding filament and sealing a drybox:

The following photo shows multiple Coupler Caps (holding filament) attached to dryboxes using my Auto-Rewinder for Ultimate Filament Drybox:

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

The following photo shows a collection of Coupler Caps - some assembled and others not yet snapped together:

To allow modifications, I have provided STEP (.stp) files.

3MF files have been provided for Prusa Slicer (has "-Prusa" in the filename) and for Bambu Studio (has "-Bambu" in the filename).

The Coupler Cap Gen 2 Bases seen in the photos were printed with Transparent Giantarm (95A) TPU with a 0.4mm nozzle at 0.2mm layer height with a 15% gyroid infill on a Textured PEI build plate with Kores glue stick applied to allow easy removal from the build plate. Supports and brims are not needed and must be avoided due to TPU's stickiness.

The Coupler Cap Gen 2 Knobs seen in the photos were printed with Orange Bambu Lab PLA Basic with a 0.4mm nozzle at 0.2mm layer height with a 15% gyroid infill. Supports and brims should not be needed.

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 AND on MakerWorld at https://makerworld.com/en/@PhilCaruso