gap i 1 b 2 c and gap ii 1 b 3 c fits the shape of the display screen 7 this makes the display screen 7 firmly clamped between the non metal block i 1 b 2 and non metal block ii 1 b 3 this cushions and protects the display screen 7 and effectively improves the service life of both of the display screen 7 and the tie down as shown in fig1 fig2 fig6 and fig7 a link rod 15 is installed on the top of the right half housing 1 b the inner end of the link rod 15 is clamped between the non metal block i 1 b 2 and the non metal block ii 1 b 3 the outer end of the link rod 15 is connected to a hook 16 the inner end of the link rod 15 is fixed to the right half housing 1 b with a screw 17 installed through the outer steel plate 10 the inner end of the link rod 15 presses against the non metal block i 1 b 2 and the non metal block ii 1 b 3 respectively when the hook 16 impacts on other things the non metal block i 1 b 2 and the non metal block ii 1 b 3 will produce elastic deformation to absorb the impact energy so as to protect the link rod 15 and hence improve the service life and the working stability of the tie down as shown.