What is Sujikai in Japanese Katana terminology?

The term "Sujikai" (筋違, すじかい) refers to a specific pattern of file marks (Yasurime, 鑢目) on a Japanese sword, where the angle is lowered from the edge (Ha) towards the spine (Mune). This pattern is often used as a decorative element on the backplate of small handles (Kodzuka, 小柄) or hairpins (Kogai, 笄). It is also used in the construction of the tang (Nakago, 茎) of the sword. When applied to the tang of a sword, the term "Sujikai" is used to describe file marks that have a steep downward slope to the right. However, in the case of small handles or hairpins, this term is used more broadly to refer to any file marks that slope downward to the right.