the woof of a woven item
緙 centers on the horizontal threads (woof) that cross the warp in weaving. The meaning is specific to textile structure.
緙 combines 糸 (thread) with 革 (leather), likely indicating a type of woven material or thread used with leather. The exact historical development is uncertain.
The left side 糸 is thread, and the right side 革 is leather. Imagine weaving horizontal threads through a leather frame to create the woof of a tough fabric.
For カク, picture a weaver using a wooden block (角, カク) to beat the woof threads into place: 角 -> カク, and the block helps tighten the weave.