Exodus 28:28

The rings of the breastpiece shall be tied to the rings of the ephod with a cord of blue yarn, so that the breastpiece is above the waistband of the ephod and does not swing out from the ephod.

And they shall bind the breastplate by the rings thereof unto the rings of the ephod with a lace of blue, that it may be above the curious girdle of the ephod, and that the breastplate be not loosed from the ephod.