1, should be smooth and smooth, no cracks, sharp edges and burned and other defects, the use of magnifying glass and other areas can be reviewed.

2, shackle to double the safety load as the test load to test. The shaft pin must not be permanently deformed and free to rotate after loosening. The length of the body length shall not exceed O.25% or O.5mm. 300 tons of the following 2 times the safety load as a test load to test, more than 300 tons of 1.33 times the safety load as a test load to test.

3, shackle can be sampling reliability test. The load is twice the test load. Shackle shall not be broken or the shackle will be damaged.

4, the use of shackle of the safety load are M (4) approved.

5, in the button body should be marked with strength level, safety load and other markings.