And they did bind the breastplate by his rings unto the rings of the ephod with a lace of blue, that it might be above the curious girdle of the ephod, and that the breastplate might not be loosed from the ephod; as the LORD commanded Moses.
Berean Study Bible (BSB) - Exodus 39:21 >Then they tied the rings of the breastpiece to the rings of the ephod with a cord of blue yarn, so that the breastpiece was above the waistband of the ephod and would not swing out from the ephod, just as the LORD had commanded Moses.