direction the spiral spring is always at a taut situation referring to fig3 the sliding disc 3 has a front direction edge seat 31 and a rear direction edge seat 32 and the front direction edge seat 31 has a through hole 313 provided on a blocking plate 312 to allow the retraction cord 4 to pass to the rear direction face and the retraction cord 4 is formed into a front direction retraction cord 4 and rear direction retraction cord with different face the retraction cord 4 is rolled at the external edge at the front direction edge seat 31 and the rear direction edge seat 32 the front direction retraction cord 4 and the rear direction retraction cord 4 are of same cord and are of equal length the retraction cord 4 uses the clip plate 321 to secure the rear direction retraction cord 4 such that the front direction retraction cord 4 will not enter into the range of the rear direction retraction cord 4 due to pulling force and the rear direction retraction cord 4 will not enter the range of the front direction retraction cord 4 in other words the lengths for both the cord are always equal accordingly when the front direction retraction cord 4 is pulled its rear direction retraction cord 4 is retracted when the front direction retraction cord 4 is at the restored position and the rear direction retraction cord 4 is at a coiled position the front direction retraction cord 4 and the rear direction retraction cord 4 are of equal length and.