Exodus 28:28
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.
Cross-references
Exodus 28:37
Parallel
Exodus 28:37 also mentions a blue lace for the turban—the same material is used here to bind the breastplate.
Exodus 39:31
Parallel
Exodus 39:31 describes a similar blue cord fastening for the turban's gold plate, both showing how specific commands were carried out.