Carbon nanoparticles, like nanocones and nanodiscs, can be obtained by mechanical treatment of carbon nanofilaments. Microstructural studies suggest that in nanocones the conical graphene stacking with progressively increasing apex (cone) angles does not fully agree with current theoretical geometry models, such as a closed cones model and a cone-helix model. The unusual stacking form of nanocones was taken into account in a modified cone-helix model. The formation mechanism of the distinctive microstructure is attributed to the inclined anchoring effect, and the relaxation of internal stresses, which were induced by the confined pyrolysis process, resulting in easier disintegration by sonication the nanofilaments. This is disclosed for the first time in literature regarding the attainment of uniform carbon nanoparticles.