Typically, shackles of this sort have a safety factor of 5, meaning that if the maximum working load is 120 tons, the minimum breaking load should be >= 600 ton

Typically, shackles of this sort have a safety factor of 5, meaning that if the maximum working load is 120 tons, the minimum breaking load should be >= 600 tons. Strictly, once the maximum working load has been exceeded, the shackle should be considered compromised. I don't have experience with any shackle on that scale, but my feeling is that you ought to be able to expect a good shackle to withstand 30 pulls to half of its minimum breaking load.