We often find that if you try to buy a shackle for Hi-Test G40/43 chain, it is hard to match the working load of the shackle to that of the G40/43 chain… So the question is why?
While digging into this we came up with a revelation, most chain specs dictate that the safety factor for chain is 4 i.e Working Load is 1/4 of the ultimate breaking strength, further chain is then proof tested to two times the working load. So for example 1/4 inch G30 chain has the ultimate breaking strength of 5200 lb and the working load of 1300 lbs (1/4 of 5200) and is proof tested to 2600 lbs, using the safety factor of 4 to determine working load.
This applies to all chain except for G40/43 chain, for some reason, that is still a mystery, the safety factor used for this chain type is 3. So in the example we just used G40/43 1/4 inch chain has the UTS of 7800 lbs only 1.5 stronger than its G30 spec, but the WLL for G40/43 chain is 1/3, not 1/4 of the UTS. Thus in our example for 1/4 inch G40/43 chain the WLL is 2600 lbs which is double the WLL for G30 chain 1300 lbs. So far I have not found why the safety factor changes for only one chain type. Chains of higher grade i.e G70, G80, G100 use the safety factor of 4. Further all chains are proof tested to 2 times the working load, except G40/43 chain, it is proof tested to 1.5 times the working load also per NACM spec .
In addition shackles use the safety factor of 5, so a Grade A 1/4 inch shackle has a WLL of 1000 and the UTS of 5000 lbs, and is proof tested to 2.2 times the working load. This is why it is difficult to find a shackle that will match the working load of the G40/43 chain. If you do decide to match the working loads there is a solution: Grade B shackle and one size bigger, these “specialty alloy” shackles are especially strong and when sized one up, match the working load on G40/43 chain.
So how does one know if a shackle is Gade B shackle? all grade B shackle pins and bolts
shall be marked with the raised or stamped letters “HS” on the head. Let us know if can add to this information…
Reference: FED SPEC RR-C-271F
NACM Welded Steel Chain Specifications