O 3 rail coupler height gauge 

3 Rail O gauge is built to standards, but unlike Scale O and HO etc, there are no coupler height gauges that I have found.

After doing some checking on my cars I believe the .688" +-.031" Center line height of the coupler appeared to be correct for the 3 rail as well as O scale. Many 3 rail coupler heights are adjustable with a little bending. I use the gauge to re-align the accidental bending over the years.To make sure all my 3 rail cars are adjusted correctly, I needed a master gauge.   

Designing a gauge, just for height, should have been easy.   I forgot on 3 rail the center rail on tubular track is "higher" than the outer rails.  The track rail insulation paper does that.  Also make sure you make the coupler the correct direction.  After a couple of iterations I came up with this.

After printing check the height from where it sits on the track to the top of the large face, it is designed to .688".  The large top face is the center of the coupler which is .360 tall.   It printed to .685 center height using PETG.  Well within the +-.031" for "center".

Testing with one of  the non-adjustable Lionel cars it looks good.

For files see the O Gage Forum 3d Printing Catalog 

Now I can adjust my cars to a master instead of car to car. 

Last update Oct 5 2022