The PWB-320XL-TRK kit includes the 4" extra large back box that has up to 2” KO’s and include flush cable-tie mounts, 4 triple play mounting solution openings for AC/AV/IT applications and three optional adjustable locking shelves for mounting equipment. Plus a powder coated trim ring for dressing the dry-wall opening. This rounded trim ring provides a generous 7/8” overlap.