Levelable and floor-decoupled 'blind' cassette for creating an inspection opening of nominal size R9 in dry or wet-cleaned floors indoors, for installation in underfloor boxes UZD350-3 in conjunction with a mounting cover DUG350-3R9 or in UGD350-3R9. Installation is carried out using leveling angles (order separately) in the aluminum frame profile of the underfloor boxes. Only suitable for smooth floor coverings.