Knuckle Coupler and Height Gauge LDraw/Studio CAD Files

Knuckle Coupler and Height Gauge LDraw/Studio CAD Files

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Knuckle Coupler and Height Gauge LDraw/Studio CAD Files

This product is a free digital download for the LDraw/Studio CAD part files for the BMR Knuckle Couplers and the Coupler Height Gauge model. No physical product is included. Note that these parts are not officially endorsed by and are provided as is. Use at your own risk.

For more info on our new knuckle couplers and a comparison between all four BMR knuckle coupler types see our Launch Article

The BMR Model Team is proud to bring you our latest product. The Knuckle Coupler LDraw/Studio CAD Files. To aid builders in designing digital models to use our new knuckle couplers we are providing these part files to the community.


BMR, in partnership with BrickForge, has been working on a replacement for the old LEGO® 9v era magnetic train couplers.

The heart of our new couplers is the Kadee® Magne-Matic Knuckle Coupler. Kadee’s couplers are the industry standard for model railroaders. They have provided reliable, trouble free operation. The specific couplers we are using are the no. 743 and no. 747 O-scale couplers. We feel these two couplers give us the best possible options for adapting to LEGO trains. They are die-cast metal couplers offering exceptional strength and durability as well as reliable operation. They are also true O-Scale, 1:48 scale couplers, which translate very closely to 8-wide LEGO scale for North American trains.

The second half of the equation for these new couplers are the draft gear boxes designed by BMR’s own Glenn Holland and produced by BrickForge. Draft gear is
the equipment that connects the coupler to the rolling stock. These draft gear boxes are injection molded in ABS plastic. We have worked hard to make sure the quality of the fit meets all expectations.

We have designed four different draft gear boxes, two for each style of coupler. These four draft gear boxes give a wide range of mounting options for your trains. The offset height of the 747 coupler is one plate higher than the 743. The S gear box has top studs for mounting, while the Z variant, named for the Z shape of the bottom gear box half, has a tile top with anti-studs on the thinner end.

These couplers are also self-centering, meaning they are spring loaded to return to the center position when uncoupled to make coupling easier.

In introducing these new couplers, we wanted to ensure they were backward compatible with all previous BMR Premium Instruction Models released. To make converting your BMR cars easy, we have produced a manual for converting all 14 of our first regular Premium Instruction models. Included are detailed assembly steps for each truck style, a parts list, and tips and build notes. You may buy a printed copy of this book or download the digital version for free.

All BMR models from here forward will include instructions for upgrading the model to the new knuckle coupler in addition to the old LEGO 9v era magnetic train couplers.


Our Knuckle Coupler LDraw/Studio CAD Files contain the following:

LDraw CAD part files for all four BMR Knuckle Couplers.

Studio CAD part files for all four BMR Knuckle Couplers with working stud connections.

Coupler height gauge Studio and LDraw model files.


Brick Model Railroader is a fan publication about LEGO® brand building bricks. 

Kadee® and the Magne-Matic Knuckle Coupler is a trademark of the Kadee Quality Products Co.

This is not a LEGO® product. LEGO, and the LEGO logo are trademarks of the LEGO Group. Brick Model Railroader, Brickforge, and Kadee are not affiliated with or endorsed by The LEGO Group.

© 2020 Brick Model Railroader LLC
and BrickForge AR LLC. All Rights Reserved.

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