A brio compatible cargo car.
I used the following tools:
3d printer (!)
Dremel with cutting attatchment
Print the following:
4x wheels (supports needed)
I used the following to make the magnetic connectors:
2x 12x3mm ring ferrite magnets with 3mm hole
2x Silver upholstery nails 11mm diameter
To make the wheel axles I used:
1x Steel spring rod 2mm diameter 100mm length
I cut the rods into 30mm lengths and smoothed off the ends using a dremel.
Alternatively you could try something like this to avoid cutting.
All parts are designed to be a tight fit (hence use of hammer!). You could add superglue for extra hold.