What do we learn from "l'Aharon ul'Vanav"?
Moshav Zekenim: This teaches that the Kusones was the same for both of them. The same applies to the Mitznefes and Avnet.
Yuma 23b brings Tana'im who argue about whether or not a Kohen Hedyot's belt was the same as a Kohen Gadol's, or if it was pure linen. (PF)