Exodus 39:20-21

20 Then they made two more gold rings and attached them to the bottom of the shoulder pieces on the front of the ephod, close to the seam just above the waistband of the ephod.

21 They tied the rings of the breastpiece to the rings of the ephod with blue cord, connecting it to the waistband so that the breastpiece would not swing out from the ephod—as the Lord commanded Moses.