Levelable cassette of nominal size R9 with cord outlet, decoupled from the floor, for the installation of installation devices in dry-maintained 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.