Abstract: A window shade detention member universally installable on a sliding flute of a upper beam to provide positioning and chained movement for window shades includes a first action side and a second action side. The first action side is located on a transverse side of a detention member and has side boards extended upwards and inwards from two sides of a base board to form a first trough and a second trough that form a transverse clipping trough which clips side wings of the sliding flute of the upper beam. The first action side also provides bucking for the chained movement of the window shades. The second action side is located on a longitudinal side of the detention member and has a third trough and a fourth trough on two ends of the connection junctures of the base board and side boards to form a longitudinal clipping trough. The longitudinal clipping trough clips the side wings of the sliding flute of the upper beam.