Connecting lengths of chain together is relatively easy if the joint does not have to pass through a windlass. The biggest problem to be faced may be finding a shackle with an end sufficiently small to pass through the eye of the chain, so that sometimes it may be necessary to use two shackles fitted back-to-back.
A few patent connectors are available for the job, such as the Mid-link, Quick-link, Lok-a-Loy and others. This photo shows one of this type. Although strong enough for anchoring they will not pass through a gypsy and tend to rust quickly
However, if the chain is used with a windlass none of these solutions is possible. The only method available is to use a pair of specially
designed C-links that can be riveted together, forming a link of the same dimensions as the chain. During the testing of anchor
connectors, see YM May 2006, two C-links were tested to destruction but their Ultimate Tensile Strength (UTS) was disappointing,
being less than half the value of the chain. Both links were bought cheaply at UK chandleries.
In view of this poor performance we decided to investigate whether C-links bought from specialist sources, both in UK and abroad,
would give better reliability than the standard items. The Internet was able to provide a number of sources, both from yachting or lifting
and hoisting suppliers, who supplied a variety of links. Many were made in USA, so postage costs need to be added if following this route.
A problem that immediately became apparent was that, although only 5/16 in or 8 mm links were purchased, they were not the same
size as DIN 766 calibrated chain. The wire size was correct but the link size was often larger than a chain link. Fortunately, most gypsies
can cope with a single link that is bigger than the chain links. During research for this article I discovered that my own anchor chain was
joined using a larger C-link. It had been in use with two windlasses for many years.
DIN 766 chain dimensions
Nominal wire thickness d (mm)
Internal length t (mm)
External width b (mm)
External length e (mm)
Similar to Crosby
What was tested
Safe Working Load
5/16 in. Connecting link.
West Marine www.westmarine.com
Forged, heat treated carbon steel
5/16 in. G-335 ‘missing link’
Selby Eng and Lifting Safety, Leeds
Forged, quenched and tempered carbon steel
5/16 in. Suncor 316-NM
Bosun Supplies www.bosunsupplies.com
Forged, stainless steel
Maillon a river Inox
Cast, bright stainless steel
(G 30 refers to Grade 30)
Cast, low carbon steel
Italy, 5/16 in.
Cast, low carbon steel
Cast, low carbon steel
8 mm chain
BS 6405 Grade 30 6156-30
Low carbon steel
Note that these links and the chain have a safety factor of 4. The Safe Working Load (SWL) is therefore one quarter of the Ultimate
Tensile Strength (UTS). Use of this equipment at loads higher than the SWL is not recommended and C-links should generally not
be used in lifting equipment, although the Crosby links came with a certificate from the supplier approving their use in lifting applications.
All links were corrosion resistant, either by being galvanised or by being manufactured from stainless steel.
We made up test pieces using 8 mm links joining two short lengths of 10 mm chain, to ensure that the link would break before the chain
did. In one case only, the single un-named 8 mm link, we used 8 mm chain because the link was too small to pass over the 10 mm wire
thickness. Each test piece was then pulled to destruction in a 50 tonne Dennison tensile test machine, at a constant strain rate of 1 mm
Most links were tested in duplicate
We also pulled a length of 8 mm chain for reference purposes.
All links were tested with a magnet to confirm their material of manufacture.
Test with Magnet
Test 1 UTS (tonnes)
Test 2 UTS (tonnes)
Mean SWL measured
ACCO chain connector
Crosby G-335 ‘missing link’
Uship Maillon a river inox
very slightly magnetic
China G30 5/16
Unmarked 8 mm
YM May 2006
8 mm chain
Molten metal poured into a mould the shape of the final object. Lowest mechanical properties.
Hot or cold metal bar is stamped or pressed into final shape. Mechanical properties improved.
Quenched and tempered
A two-stage heat treatment process that maximises strength and toughness.
Various processes that may include quenching and tempering, that improve toughness and strength.
Low carbon steel
Also known as mild steel. General purpose steel with carbon content below 0.2%. Not hardenable by heat treatment.
Carbon content above 0.2 %. Heat treatable.
Non-magnetic grades are not heat-treatable. Cold forging can induce slight magnetism in some grades.
The difference between heat-treated and cast links was immediately apparent when we riveted them to join the two halves together. Whereas the cast ones required only a couple of taps with a hammer to press the rivets down into their countersunk holes, the heat treated links took considerable effort and a number of heavy blows using a steel drift. This is not a job that should be done on board.
The C-links we tested fall into several distinct groups.
- Firstly, there is the fully identifiable industrial type, made of carbon steel using the optimum metallurgical processes of forging and subsequent heat treatment. The ACCO and Crosby fall into this group. The industrial C-links came with documentation that included the SWL and other information. Our test programme has found these links to be virtually as strong as the chain and therefore perfectly acceptable for anchoring use.
- Secondly, the stainless steel types. These appear to have been aimed at the leisure marine market. The emphasis has been put on their corrosion resistance, rather than their strength and thus the stainless steel links were weaker than the carbon steel types. The Suncor links failed to reach their advised strength although the values achieved were reasonable and repeatable. They were easier to assemble than the carbon steel links and could be an acceptable compromise for the yachtsman.
- Thirdly, various miscellaneous low-carbon, cast types. Many are made as cheaply as possible and are often the ones on sale in chandleries. They can be difficult for the yachtsman to identify. Two of them, ‘China G30’ and ‘5/16 Italy’ were probably made to match the Grade 30 specification for low-carbon chain. The two ‘China G30’ links were bought in a chandlery with no documentation. The China link that failed at the lower load appeared to be rather brittle, suggesting that heat treatment had not been carried out correctly. Although the mean UTS was good the lower value was below the required strength. The two links tested in the YM May 2006 tests, and our only unmarked link, failed at an unacceptably low figure. The blackening of the unmarked link’s fracture face is almost certainly due to poor quality material, containing slag and oxides. The single link marked Italy was slightly disappointing, although still acceptable for the majority of anchoring applications.
This C-link was particularly poor, failing at a low load and appearing to be largely composed of slag.
On inspecting the failed links we can see immediately that their fractures differ. The more ductile stainless steel links deformed but none fractured across the wire diameter, whereas the steel links all fractured in a more brittle manner. If all links had the same strength, the more ductile ones would be better in shock loading, such as snatching in waves. Taking the strength into account, a chandlery-bought stainless steel link is probably better than a chandlery-bought steel one but not as good as a specialist heat-treated one.
The reference chain failed in a ductile manner, with considerable deformation before fracture. This behaviour augurs well for snatch loading and shocks.
Heat-treated, carbon steel C-links that are marked with a load standard are virtually as strong as the chain which they join. Provided they will pass through the gypsy, which most will, they are fully acceptable for yachting use.
Stainless steel C-links are less strong than carbon steel equivalents but are adequate for general use. Although they will not rust in normal anchoring use, they can promote increased rates of zinc loss from attached chain, by galvanic action. Use them with caution.
Links of the type often seen in chandleries, unmarked and of unknown origin, should be avoided. Many seem to be badly made, of inappropriate materials, and to use them for anchoring would be risky.
Since this work was carried out there have been some changes so far as manufacturing is concerned. It appears that ACCO have been bought out by Peerless and manufacture has been transferred to the Far East. The C-links now sold by West Marine appear to be fully satisfactory. I intended to test them until I found that delivery would cost $70.
I have found a UK supplier who is prepared to sell single items by mail order, no minimum order. The company is Tecni-cable, based in Somerset. See http://www.tecni-lift.co.uk/Products...5-Missing-Link. Listed under Crosby products or search G335 from the home page. They will carry sufficient stock for the likely numbers required by yacht owners, in 8, 10 and 13 mm sizes.
Some buyers have reported that the Crosby links will not articulate correctly in the final links of the chain being joined. This is probably because the Crosby links are made to a USA standard, not a metric one. The solution is simple. Squeeze the final link of the chain in a vice to open it up a little. Grades 30 and 40 chain are in the normalised condition and will not be harmed by this minor deformation. The chain will still pass through a windlass.
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8 mm chain with internal width 10 mm. Crosby C-links require slightly more, maybe 10.5 mm.
Final link of the chain being squeezed in a vice. I needed to slip a length of pipe over the vice handle to deliver sufficient torque.
Final link width is now 12 mm. Damage to the chain is minimal, although this sample chain is well used and some surface deposit has flaked off.
Some C-links are extremely susceptible to corrosion. This does not appear to be for galvanic reasons but simply because the cheaper versions are made from poor quality steel without any alloying elements that might protect them. Frequent inspection is advised, especially for chain that may have spent a winter in a wet anchor locker. Two examples to illustrate this:
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It might be supposed that some form of galvanic reaction between the C-link, galvanised and stainless steel chains might be responsible for corrosion of the C-link.
However, in this case both chains are galvanised and the zinc on each appears to be intact. The corrosion is simply due to the poor electroplated zinc coating on the C-link and highly vulnerable steel of manufacture.