N 6820 has an adjustable steel housing with a 1-7/16 in ball bearing roller installed. Used on charmed mirrored doors in the late 90's, the original designed housing is no longer available. In some cases, to make this part work the lower tabs may need to be trimmed off. Never remove the upper tabs nearest the adjusting screw. The housing upper tab snaps into a slot on the inside of the door frame, while the door rests on the bottom tabs that extend out from the base of the housing.