Originally Posted by MeiWenti
Noelex - we were looking at a Wichard HR shackle as our chain is 8mm G70, so a standard 8mm shackle is relatively weak compared to the chain. However, Wichard don't do allen-headed HR shackles so we would need to go with the cut and drill solution. However, I wasn't aware of concerns about the 17-7 HR steel
- what's the problem with it?
The concern is the lower corrosion
resistance. In simple terms crevice corrosion
is the greatest problem, but there are other more complex types of corrosion. 17-4 (630) stainless steel
is more vulnerable to this type of corrosion than 316.
Anchor shackles can spend some time burried under the substrate in an oxygen low enviroment, or retain mud on the shackle when retrieved.
Rusting of steel is very obvious. In addition the corrosion is reasonably uniform, stainless steel is exactly the opposite pits form and grow at right angles to the surface being attacked. Thus it is easy to miss the development of a problem.
However, I stress I am no expert in metallurgy. It is difficult to gain a perspective if this is a practical problem, but there are reasonable alternatives which do not have these issues.
I also use G7 chain (10mm) and my solution was to use a G8 shackle with the pin modified as shown. My current
shackle is a Crosby G-209A (these are a similar, or slightly higher strength than HR SS). There are similar products from a Green Pin.
Another option is to use a titanium shackle. Wichard make some, but not with a flush pin. They are not as strong as the HR option, but I suspect it would be adequate (aim for a bit of overkill to have some allowance for side loading). Titanium does not have any corrosion problems.