Corrosion disc is the correct term. While its a good idea to utilize them, I honestly haven't seen much of an issue when they aren't used. Consider the fact your studs are steel and touching the aluminum rims, as are the lug nuts.
Way it was explained to me years ago, 1 full thread must protrude beyond the lug nut.
My first Truck had 7 aluminums, and 1 steel inner on Drives. It actually had a metal spacer,between the two dissimilar ones. Purpose of it, to keep tire treads lined up. First and last time I saw that. Immediately bought an aluminum and switched it out.But such a “ spacer” does exist.Usually, You can put an inner steel, and an outer aluminum w/o changing studs.2 aluminums- new longer studs. On a trailer, It’s not much more to buy a new hub, with longer studs. Especially if you’re paying labor rates for the job. Doing yourself, sometimes you can knock old ones right out with a sledge, and buzz new ones in place using gun on spacer/ sleeve/ nut. If you’re lucky, still at $8 or so ea. It adds up.