chain, tip of a scabbard, flatiron
鐺 centers on metal objects with a connecting or enclosing function: a chain, the metal tip of a scabbard, or a flatiron. The meanings are loosely connected through metalwork and practical tools.
鐺 combines 金 (metal) with 當, which likely contributes the sound. The exact historical development of the meanings is uncertain.
The left side is metal 金, and the right side 當 looks like a roof over a field. Picture a metal chain used to secure a roof, a metal tip protecting a scabbard, or a flatiron pressing clothes under a roof.
For ト, imagine a metal toe ring made from a chain: toe -> ト, and the metal chain wraps around the toe.