T3D-041-004 NEM HST / Mk3 Coach Couplings (Slidedoor)

Trackside 3D SKU: T3D-041-004

$2.99 USD

Available Now!

Trackside3D magnet coupling kit for the Hornby HST Power Cars and newer Mk3SD (slide door) coaches with NEM pockets. These are designed to work with any Hornby HST power car with the bogie mounted NEM pocket. This design works for the newer Mk3SD coaches (slide door) with the chassis mounted NEM pockets. If your NEM pocket is mounted to the bogie of the coach, you most likely have the older Mk3 (Slam door coaches). For slamdoor NEM Mk3 coaches, you will want the T3D-041-000 pack which has a similar coupling design specifically designed for the Mk3 slam door coaches. 

Note: We are currently working on a Mk3SD version of our T3D-041-000 design, so if your preference is for that design, check back soon as we have many new designs in development and test.


These models should be 3D printed upright with the open end of the cylinder facing sideways with supports enabled. You can use the Trackside3D small object profile with supports, but reduce the print speed to 10mm/sec except for travel which can be left as-is and enable retraction on layer change.

This pack comes with the following models:

  1. HST Power Car Standard Coupling
  2. HST Power Car Wide Coupling (same length but slightly wider)
  3. Mk3 Coach Standard Coupling
  4. Mk3 Coach XC Coupling
  5. Mk3 Coach Standard Coupling with wider NEM wedge

The "wider" coupling designs are provided for those who have problems with the normal couplings in the power cars or slide door Mk3 coaches. We have found that some sets have slightly out of spec NEM pockets, so the wider NEM wedge (fraction of a mm wider) fixes this problem preventing the coupling from falling out in motion. You should start with the standard version and if you have issues with the couplings falling out of the NEM pockets, try the wider version.

There is no cap with this design, if you wish to hide the shiny magnet, you can use nickle brushed magnets or simply use a black permanent marker to mark the exposed side.

All of our magnetic couplings are designed to be easy to build:

  • Download and Print
  • Remove the brim
  • Select your magnet
  • Push to install the magnet
  • Slide coupling into your rolling stock

Compatible Magnets:

  • 3mm diameter cylinder magnets (1/8" also fit)
  • Up to 6mm in height, recommend 4mm
  • Use axial magnets for polarity couplings
  • Use diametric couplings for non-polarity couplings

If you are planning to build a lot of couplings, we recommend you look at our magnet polarity tool 028-009.

Design Features:

  • Coupling connection "floats" to expand around tight curves
  • Designed for magnetic auto-uncoupling
  • Designed to balance when connected
  • Designed with a coupling action when magnets are in proximity
  • More prototypical look
  • NEM Wedge near edge of pocket for snug connection but easy to remove

Trackside3D have developed a technique for printing NEM couplings on filament printers such as the Creality Ender 3. For more information on this technique and how to successfully print NEM couplings on your filament 3D printer, please visit https://oorail.co.uk

 Model Dimensions Print Time Material Usage
HST Wide 5x17.1x9mm 11 minutes 0.13m (< 1g)
HST STD 5x17.1x9mm
11 minutes 0.13m (< 1g)
Mk3 Wide
6 minutes 0.07m (< 1g)
Mk3 STD 5x17.1x5mm
6 minutes 0.07m (< 1g)
Mk3 XC 5x16.2x5mm
5 minutes
0.07m (< 1g)
  1. Trackside3D Small Object Profile
  2. Supports Enabled
  3. Build Plate Adhesion - brim
  4. Infill = 100%
  5. Layer Height between 0.1mm (or better)
  6. Print Speed = 10mm/sec or slower