PUKX 25 – Low-profile cable grommet

PUKX 25 (/pʌks/) is a low-profile cable grommet designed for cables up to 6 mm in diameter. It installs in a 25 mm (roughly 1 inch) through-hole. The concept evolved from my Generic Studio Arm Mounting Grommet,. This all-new design features multiple components that allow optimal print orientation for optimal strength and printability. The multi-part approach also enables subtle color accent possibilities.

This model is intended to be the starting point for extension that utilize the same core dimension, provided are specifications for the cap and ring components, which can easily be adapted for more specific applications such as cable compartments or smartphone holders. Also included is a fully parametric Autodesk Fusion file that makes customizing critical aspects—like thread length or cable guide shape—effortless.

Print Instructions

I printed all my variations of this model in PLA; ASA/ABS will work nicely as well. I'd advise against using PETG, as its toughness makes it prone to seizing under mechanical friction.

All parts are already oriented in their optimal print orientation. No supports required.

The hub-halves are placed close to each other to keep the otherwise exposed lenghts from lifting. A small gap of 0.1 mm works well to join the heat zones of both parts without fusing them together.

While this design is optimized to be printed with a 0.4 mm nozzle at a 0.2 mm layer height, only the ring part really benefits from this. In general just use your preferred profile with as much perimeters as needed to saturate the first few layers on the nut part.

Installation Process

Setting up a PUKX 25 cable gland requires careful execution to ensure a flush fit. This section covers the correct hole size and assembly order to prevent misalignment or the need for rework—especially important in tight spaces.

Drilling Holes

PUKX 25 is designed to be matched with a perpendicular 25 mm through-hole in a board with a thickness of up to 16 / 25 / 38 mm (5/8, 1 or 1 1/2 inch respectively). Holes like this are typically drilled with a Forstner drill bit. If you are drilling free-hand and are not sure that you can manage to get it perpendicular, opt for a slightly bigger hole (26 mm) to have enough wiggle room for the insert to sit parallel to the surface. 

Order of assembly

The following installation sequence is carefully outlined to minimize frustration during assembly. Performing the steps in the specified order ensures that all components are properly positioned, avoiding the need to disassemble and rework—especially important in confined spaces.

1. String the nut onto the cable

2. Feed the cable through the hole

3. Place the ring onto the cable

4. Run the cable through the cap

5. Place the hub halves around the cap

6. Seat the ring to secure the hub-halves

7. insert the assembly into the hole

8. Tighten the nut (use the installation tool if needed)

Design Features

No feature on this design is an accident. This section gives a brief overview of the most relevant aspects and the thought process behind them.

Optimal Print Orientation

Finding the optimum here is always a trade-off between printability, surface quality, and durability. The requirement to install a cable with connectors on both ends necessitated a split design, leaving two main options to consider: printing the hub halves upright for optimal printability of internal features that interface with the cap part, or printing sideways to align the applied force from the nut perpendicular to the layer lines. The latter approach makes the interface with the cap part an overhang. After prioritizing the various constraints, the consequential drawbacks were addressed through design adaptations.

Printable Overhangs

Design for 3D printing requires techniques to keep overhangs exceeding certain limits. Steeper faces require either bridgeing or supports. The former is a unavoidable nuisance, while the latter is an admission of inability. While a 50-degree overhang angle is generally considered safe, having interfacing parts printed in different orientations further limits possible geometry. A 45-degree angle is beneficial in this case, as its counterpart is also 45 degrees and can thus be printed in a wide variety of orientations. This provides maximum flexibility when designing individual components.

Controlled Bridging

Printing circular geometry perpendicular to the build plate always presents the challenge of overhangs that exceed the printable overhang angle. This can significantly impact print accuracy. Added supports can mitigate this problem but represent wasted material when an engineered solution exists. Teardrop shapes eliminate non-printable overhangs but weren't viable in this case as they require significant extra height. The next best solution is flat sections that enforce bridging.

Small Feature Elimination

Printing threads sideways has the disadvantage of generating small islands in the top layers. The top section of printed threads is the weakest part and not particularly useful anyway. Tiny features like these have a high chance of producing unwanted print artifacts. A dedicated cut operation was used to remove the affected area.

Printable Threads

Standard threads from most CAD tool libraries have a 60-degree tooth angle. Combined with the thread pitch angle, this is printable in most cases but not the cleanest. This incentivizes designing custom printable threads, which isn't overly complicated. In Autodesk Fusion, this can be accomplished various ways. The approach taken here uses a Box Section Spiral with chamfered edges and a combination of various extrudes. With this procedure, overhang angles can be limited to the target angle of 45 degrees and will cleanly recalculate with parameter changes.

Chamfers on All User-Contact Surfaces

For better handling, all edges that users might touch are chamfered to at least two layers (0.4 mm respectively). This is sufficient to eliminate unpleasantly sharp features. Faces touching the build plate are prone to elephant foot, which makes them extra sharp. On the hub parts, this defect might also interfere with mechanical operability.

The Installation Tool

Testing revealed a fundamental installation problem: when tightening the nut, the entire assembly would often spin freely instead of the nut threading properly. This happens because friction between the nut and hub exceeds the friction holding the hub to the table. The solution required a way to independently grip and stabilize the hub during installation.

The custom installation tool solves this with a dual-purpose design. It locks into notches at the hub's base to hold it steady, but also flips to serve as a nut wrench. The spring-loaded design automatically grips the hub when inserted and releases easily when used as a wrench. The raised handle provides comfortable leverage, while an anti-twist tab and slot prevent the tool from twisting under load.

Customization

Extensibility of this design was a welcomed byproduct of the shape that was found. The ring part rotates freely around the hub and is held down by the cap; This allows for various alteration like containers for cables or a mouse bungee maybe. The cap part could be modified as a smartphone holder.
Down below are the drawings with all critical dimensions of the cap and ring part.

The F3D file for the assembly and STEP files for the cap, ring and nut parts are available for download.

Apart from this model being a baseline for the PUKX 25 system, the Fusion file is parametric and can be used to generate insert for larger holes in thicker boards. Parameter names starting with _ are model-internal calculations or are there for documentation purposes, don't change these. All other parameters can be modified.

History

• 2026-04-19 feat: @Ahrimaan suggested that it would be nice if the two hub halves stayed together; a clamping ring and a matching groove have been added; the updated version is now available for download in the "Beta Release" folder.

• 2026-03-29 fix: wrong chamfer dimension on one of the hub halves

• 2026-03-28 Publication of the first Release

• 2026-01-12 First draft based on GSA1

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