וַיִּתְּנ֤וּ עָלָיו֙ פְּתִ֣יל תְּכֵ֔לֶת לָתֵ֥ת עַל־הַמִּצְנֶ֖פֶת מִלְמָ֑עְלָה כַּאֲשֶׁ֛ר צִוָּ֥ה יְהוָ֖ה אֶת־מֹשֶֽׁה׃ (ס)
And they tied unto it a thread of blue, to fasten it upon the mitre above; as the LORD commanded Moses.
Read halakhic rulings (Jewish law) on Exodus 39:31: and classical halakhic sources.