We custom make the chain markers for all chains 13mm upwards as from our experience, even those chains which are sold as calibrated chain, ie calibrated DIN766 anchor chain, and manufactured within the same chain specifications are not the same dimensions.
What's our justification for saying this?
Having worked with the owners, crew and builders of larger boats over the past couple of years we have found that there is no standard marker which will fit all chains of the same calibrated size. So for example, for calibrated 14mm anchor chain we currently have 15 different designs to draw from and are adding more as owners come in with their calibrated chain of a different dimensions.
Even when speaking to the manufacturers they will not provide a chain link dimensions unless they go and measure it for that particular batch of chain.
So if they are calibrated, why the difference?
Simply put, the DIN766 specifications allows for a considerable amount of tolerance in the chain link width. We're going to look at 14mm chain in the following example.
If you take a look at a typical diagram for 14mm chain pulled from one of the largest chain manufacturers in Europe...
you can see the chain link width is indicated as a maximum outer of 50mm and a minimum inner of 17mm.
Logically if the wire diameter (width of the metal forming the link) is 14mm and the outer width is 50mm then the inner width would be the outer width minus two sides of the link, so 50-14-14 which is 22.
This is 5mm larger than the minimum inner width of 17mm, but is still within the specifications. On top of that there's an allowable tolerance of 0.6mm in the wire diameter which could add another 1.2mm onto the inner width variance. So for 14mm calibrated chain there's a potential difference of 6.2mm allowed within the calibrated DIN766 specifications.
The pitch (inner length) should always be around 41mm, but this is also not the case. We have been provided with pitch lengths ranging from 37mm through to 42mm by owners.
Why does this matter?
The chain link dimensions are really important for us to provide a proper-fitting chain marker. If we make a standard chain marker for 14mm there's a good chance it will not fit the chain. Make it too large and it simply will not fit into the link, too small and it may get punched back out.
In fact from our 14mm chain customers so far the inner width has varied from 15.7 through to 21. Throw in the variations in pitch and hey presto...there's no such thing as a standard calibrated chain from our perspective.
And that's why we custom make all of our larger anchor chain markers for the customer's boat.