This is an track adapter to connect the pre-1991 "blue-area" (or gray-area) tracks with the newer RC / Power Function tracks (and also possibly 9V tracks, although I haven't tested this). I designed the adapter so my son could use my old blue-area tracks with the ones that came with this Lego City RC train.I slice the STL with Slic3r 1.1.7 using the following settings: Note that I drew the lego knobs slightly smaller than their true size (4.6 mm vs 4.8 mm) to compensate for my 0.4 nozzle extruding small features slightly larger than they are. Also, the STL does not compensate for ABS shrinkage, which is 0.5%. So you either need to scale the STL by 1.005 if printing with ABS. Personally, my ABS settings simply include the commands M92 X80.4 and M92 Y80.4 (assuming the original value was 80) at the beginning of the generated G-code to perform the scaling in x- / y- direction.