This is 3D printed shell for an N scale version of the ubiquitous Ruston 48DS shunting locomotive. It is designed to fit the TU-7T chassis from Japan which is about the only decent chassis small enough. You will also need some lead or tungsten weight to put over the chassis and to do a spot of filing to make it all fit as it's not quite possible to print it to fit as is.
Note that the TU-7T is a 4.5v chassis so you should also fit either a resistor or limit the voltage.