sentence: Filaments containing selected segments were then re-extracted using a 686-pixel box size with an inter-box distance of 73 Å. Similarly , with G51D and WT dataset , an initial 3D reference was de novo generated by relion_helix_inimodel2d using selected particles comprising an entire helical crossover , and the initial 3D model low-pass filtered to 60 Å was then applied further as a reference map to perform de novo 3D classification .