Originally a door pivot, now mostly figurative for a critical control point. Key compounds: 枢纽 (hub, linchpin) and 中枢 (central nervous system; nerve center of an organization).
Left wood radical. A door pivot was a wooden post, so the radical records the original physical object. It groups 枢 with other wooden-structure characters like 柱 and 梁.
Right 区 supplies the sound - qū drifting to shū, a moderate shift. It contributes no meaning here and is a contracted simplified form replacing the fuller phonetic in traditional 樞.
