This is sliding hatch cover as used on some early LNER planked end vans. It is designed primarily to be used on the 4mm Parkside LNER planked van kit to enable conversion to other prototypes. Use pictures for reference and pay close attention to details such as corner strapping and the angle of the end of the headstocks, as well as brake gear used on the chosen prototype. It will print on FDM machines but use a 0.2mm nozzle and as small a layer height as possible. I have successfully printed it on an Ender 3 S1 using 0.04mm layer height.