וַיִּרְכְּס֣וּ אֶת־הַחֹ֡שֶׁן מִטַּבְּעֹתָיו֩ אֶל־טַבְּעֹ֨ת הָאֵפֹ֜ד בִּפְתִ֣יל תְּכֵ֗לֶת לִֽהְיֹת֙ עַל־חֵ֣שֶׁב הָאֵפֹ֔ד וְלֹֽא־יִזַּ֣ח הַחֹ֔שֶׁן מֵעַ֖ל הָאֵפֹ֑ד כַּאֲשֶׁ֛ר צִוָּ֥ה יְהוָ֖ה אֶת־מֹשֶֽׁה׃
And they did bind the breastplate by the rings thereof unto the rings of the ephod with a thread of blue, that it might be upon the skilfully woven band of the ephod, and that the breastplate might not be loosed from the ephod; as the LORD commanded Moses.
Targum Jonathan on Exodus
and fitted the breastplate by its rings to the rings of the ephod by a ribbon of hyacinth, that it might adhere to the band of the ephod, and that the breastplate be not loosened from being upon the ephod, as the Lord commanded Mosheh.