Exodus 28:23

על החשן means [AND THOU SHALT MAKE] FOR THE BREAST-PLATE (not upon it), — in order to fix them on it. And it would not be correct to say that this means that they should originally be made upon it (על), for if this were so why should it again say in this verse, “And thou shall put the two rings [on the two extremities]”? Would they not already have been lying upon it if they had been made together with the breast-plate? It should rather have written at the beginning of the verse, “And thou shalt make at the ends of the breast-plate two rings of gold.” In the case of chains, also, you must explain it similarly. על שני קצת החשן ON THE TWO EXTREMITIES OF THE BREAST-PLATE — on its two corners that are close by his neck, on the right and on the left, which come opposite the shoulder-pieces of the ephod.

וְעָשִׂ֙יתָ֙ עַל־הַחֹ֔שֶׁן שְׁתֵּ֖י טַבְּע֣וֹת זָהָ֑ב וְנָתַתָּ֗ אֶת־שְׁתֵּי֙ הַטַּבָּע֔וֹת עַל־שְׁנֵ֖י קְצ֥וֹת הַחֹֽשֶׁן׃

And thou shalt make upon the breastplate two rings of gold, and shalt put the two rings on the two ends of the breastplate.