From zarar (in the sense of scattering); a chaplet (as spread around the top), i.e. (specifically) a border moulding -- crown.
see HEBREW zarar
H2213. zer
זֵר noun masculine circlet, border (originally that which presses, binds, compare also Aramaic bracelet, זִירָא wreath, crown, Late Hebrew זִיר id., זִירָה ring, wrestler's ring; others from a √ זרר) — זֵהָב זֵר Exodus 25:11, 24, 25; 30:3; 37:2, 11, 12, 26; זֵרוֺ 30:4; 37:27 (all P).