The kit comprises a closure part (8) retaining profiles which can form a frame element (6) secured via coupling fittings. The closure part, inserted in the frame element via sealing profiles (10), consists of hollow (11) and rod-shaped profiles (12). Pref. the frame element is composed of a profiled tube (7), held by screwed coupling and contg. a screw and a holding duct, with mitred abutments. The screw duct in the profiled tube(s) may have a round cross-section with a longitudinal aperture, with a concentric screw retaining bore with straight side walls.