which protrudes beyond the base plate 1 a through the recess 6 and a bumper 9 limiting the range of hook 7 pivoting the arched arm of the hook 7 and the guide pin 8 mate the guide 4 and the friction spring 5 the base plates 1 a and 1 b at one end have fasteners 10 a and 10 b for securing external cover members at the same time after securing the plate 1 a to the side member of a window frame the fastener 10 a is located above the sash rotation axis whereas after securing the plate 1 b to the side member of a sash the fastener 10 a is located below the rotation sash axis at the side with the fastening member 3 the base plate 1 a has a guide 18 mounted along the bottom edge of the base plate 1 a restricted at one end by the holder 11 the slide 13 in the form of a rod 13 u2032 moves along the guide 18 the rod 13 u2032 is secured with one end to a seat 13 u2033 while its other end slides through a hole in the holder 11 a spiral spring 12 is slid over the rod 13 u2032 one side of the spring 12 is engaged at the free end of the rod 13 u2032 and its other side rests against the holder 11 the seat 13 u2033 is connected to a pivoting catch 16 mating the guide pin 8 pivoting of the catch 16 is limited at one side by a cut out in the seat 13 u2033 when a window sash is taken.