Rashi on Leviticus 8:9/רש"י על ויקרא ח׳:ט׳

1וישם על המצנפת UPON THE MITRE … DID HE PUT [THE GOLDEN PLATE] — Threads of blue purple that were: fastened on the Plate he put over the mitre, consequently the Plate hung from the mitre mid would be “against his face” (upon his forehead) as stated here (cf. Rashi on Exodus 28:37).