Lock fitting for frame construction parts adjacent to one another, comprising - an inner part (1, 1') as a first construction part having an at least sectionally flat rectangular cross-section, - an outer part as a second construction part, which flanks the inner part (1, 1') in the area of its flat rectangular cross-section, and - at least one twist lock element which has = a disc-shaped twist lock body being rotatably guided in a circular guide contour of the inner part (1, 1') and adjacent to the lateral surface of the inner part (1, 1') which is flanking the outer part, as well as = an eccentric surface applied to a circumferential section of the twist lock body and recessing, which in the unlocked position of the twist lock body essentially is aligned with the flanking lateral surface of the inner part (1, 1'), and which in the position of the twist lock body locked by a rotation of the twist lock body shifts into the guide contour of the inner part (1, 1') such that the twist lock body acts upon the outer part in a locking manner with its flank adjacent to the eccentric surface, characterized by - a formation of the twist lock body in the area of the flat rectangular cross-section of the inner part (1, 1'), cut out of the material of same through a cut contour and hence formed in one piece, and - a holding bar between the twist lock body and the inner part (1, 1',) bridging a recess in the inner part (1, 1'). - an inner part (1, 1') as a first construction part having an at least sectionally flat rectangular cross-section, - an outer part as a second construction part, which flanks the inner part (1, 1') in the area of its flat rectangular cross-section, and - at least one twist lock element which has = a disc-shaped twist lock body being rotatably guided in a circular guide contour of the inner part (1, 1') and adjacent to the lateral surface of the inner part (1, 1') which is flanking the outer part, as well as = an eccentric surface applied to a circumferential section of the twist lock body and recessing, which in the unlocked position of the twist lock body essentially is aligned with the flanking lateral surface of the inner part (1, 1'), and which in the position of the twist lock body locked by a rotation of the twist lock body shifts into the guide contour of the inner part (1, 1') such that the twist lock body acts upon the outer part in a locking manner with its flank adjacent to the eccentric surface, characterized by = a disc-shaped twist lock body being rotatably guided in a circular guide contour of the inner part (1, 1') and adjacent to the lateral surface of the inner part (1, 1') which is flanking the outer part, as well as = an eccentric surface applied to a circumferential section of the twist lock body and recessing, which in the unlocked position of the twist lock body essentially is aligned with the flanking lateral surface of the inner part (1, 1'), and which in the position of the twist lock body locked by a rotation of the twist lock body shifts into the guide contour of the inner part (1, 1') such that the twist lock body acts upon the outer part in a locking manner with its flank adjacent to the eccentric surface, characterized by - a formation of the twist lock body in the area of the flat rectangular cross-section of the inner part (1, 1'), cut out of the material of same through a cut contour and hence formed in one piece, and - a holding bar between the twist lock body and the inner part (1, 1',) bridging a recess in the inner part (1, 1').