Exodus 39:21 in the King James Version
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.
Context
20 They made two more rings of gold, and put them on the two shoulder straps of the ephod underneath, in its front, close by its coupling, above the skillfully woven band of the ephod.
21 They bound the breastplate by its rings to the rings of the ephod with a lace of blue, that it might be on the skillfully woven band of the ephod, and that the breastplate might not come loose from the ephod, as the LORD commanded Moses.
22 He made the robe of the ephod of woven work, all of blue.