accommodated with a ball 141 which is abutted with an elastic element 142 and the actuating part 133 is formed with a latching groove 136 to accommodate the ball 141 the control slot 13 is opened with a locking groove 15 in a direction perpendicular to the inner wall 134 an interior of the locking groove 15 is accommodated with a ball 151 which is abutted with an elastic element 152 and the actuating part 133 is formed with the latching groove 136 to accommodate the ball 151 referring to fig2 2 a 4 5 and 6 at a same time it shows a first three dimensional exploded view a second three dimensional exploded view a first schematic view of an operation a second schematic view of an operation and a third schematic view of an operation of a preferred embodiment of the present invention as shown in the drawings the present invention includes the knob 131 which uses the ball 141 in the locking groove 14 to lock the knob 131 in the control slot 13 besides the ball 141 in the locking groove 14 is also abutted with the elastic element 142 allowing the knob 131 to be more effectively locked in the control slot 13 moreover the actuating slot 11 of the present invention is provided with the actuating rod 111 and the end of the actuating rod 111 is formed with the teeth part 112.