A vessel lost one anchor and four lengths of chain cable during anchor handling. During the vessel’s previous drydocking, a number of chain cable lengths had been renewed on port and starboard side, including a number of Kenter shackles (joining shackles) as found necessary, due to wastage in excess of allowable limits. The remaining part of the anchor chain cable lengths and Kenter shackles were at that time found to be in satisfactory condition.
One anchor and four lengths of chain cable had to be replaced, including Kenter shackles. The probable cause of the damage was the fracture of a Kenter shackle. According to available information, the loss of anchor and chain cable lengths was attributed to the fracture of one of the Kenter shackles that had not been renewed in drydock.
The intricate shape of the various parts illustrates how large forces are to be transferred through relatively small contact areas, and proper design and well machined faces and corners are very important for the durability of such shackle.
Experience has shown that a number of anchors and chain cable lengths have been lost due to failure of Kenter shackles, where fatigue cracks have developed from poorly designed machined faces and corners.
In the above case it is assumed that the failure may be attributed to mishandling of the Kenter shackle during opening/fitting operation. Since in most cases Kenter shackles on old anchor chains are rusty/frozen, and opening up and reassembly requires the use of heating or mechanical force, cracks are likely to develop and should result in replacement rather than re-use.
When a chain cable length is replaced due to wear and tear, the Kenter shackle(s) are normally worn as well and should be replaced.
Source: DNV
Officer of the Watch 
very valuable & informative!!