crevasses which stary wet (cracks, welds, shackle threads, keel bolts, etc.) or confined spaces (swivel shafts, etc.). Corrosion may also happen internally. Welding may cause the cromium to bind with carbon and thus indirectly lead to corrosion. In come cases the shaft is threaded with a nut welded onto it to hold the two bits together. First of all, a threaded bar is inherently weaker than a solid bar of the same diameter. Then there is the issue of the welds not holding. When a boat swings on a well-embedded anchor, this can cause strong lateral loads on the swivel, causing its jaws to be prized open - thus disconnecting the chain from the swivel. Hence the above advice from Rocna. Some boating schools teach that the anchor should be pulled tight against the bow roller by the windlass. This causes stress to the weakest link (swivel) as the vessel pounds though waves and can thus speed up failure. See also Slewing bearing References Bibliography Blackwell, Alex & Daria; Happy Hooking – the Art of Anchoring, 2008, 2011, 2019 White Seahorse; Hinz, Earl R.; The Complete Book of Anchoring and Mooring, Rev. 2d ed., 1986, 1994, 2001 Cornell Maritime Press; External links Joining Mechanical engineering