The differentiation such as tachi or katana is also attributed to the fittings of each sword, and the blades themselves were rather similar and shared commonalities (however, blades had shapes that suit their respective needs, which were taken into account in fabrication).
太刀や刀という区別も、外装が持つ属性に起因するもので、刀身自体に互換性が無いほどの差異がある訳では無かった（もちろん、それぞれに適した刀身の姿があり、制作時にはそれに則って作られている）。