ornamental hairpin
釵 centers on a decorative hairpin, typically made of metal, used as an ornament.
釵 combines 金 (metal) with 叉, which likely contributes the sound and the idea of a forked or pronged shape, describing a metal hairpin.
The left side is metal 金, and the right side 叉 looks like a forked prong. Picture a metal hairpin with a decorative forked end.
For サイ, imagine a sigh of relief as you finally find the perfect ornamental hairpin: sigh -> サイ.