Ṭayy al-biʾr is the fitted masonry inside a well, stabilizing its structure. Maḥāl are the back’s vertebrae, while al-ḥaniyy evokes curved bows. One image expresses a tightly connected backbone; the other expresses its organized curvature.
The important difference is between firm assembly in stonework and functional bending in bows. Together they communicate strength that still supports motion.