Exodus 28:27-28

27And two other rings of gold you shall make, and put them on the two shoulder straps, underneath the ephod toward its front, right at the seam above the intricately woven band of the ephod.

28They shall bind the breastplate by means of its rings to the rings of the ephod, using a blue cord, so that it is above the intricately woven band of the ephod, and so that the breastplate does not come loose from the ephod.