Aspect ratio is one of the most important concepts of chain maille to understand, and can also be one of the most difficult to understand. Aspect ratio is important for selecting the right ring for the right job. Aspect ratio is the ratio of the Inner Diameter of a ring, shorthanded ID, to the Wire Diameter, WD. This ratio controls how tight or loose a particular weave will be, or if the weave can even be made, as all weaves have a minimum AR. This is because if the AR of the rings is too small, as subsequent connecting rings are added to a weave, the space necessary to complete the next connecting ring will shrink until the next ring can no longer be added and the whole weave binds up. Even though all weaves have a minimum AR, most weaves do not have a maximum AR, but, there will be a point where the weave becomes unattractive and loose, due to the excessive amount of space between connections. There is a point, or a range of points, between too small and too large where the weave will be the most aesthetically pleasing and is typically labeled ‘recommended’ or ‘preferred’ AR.
Here is a fun little diagram demonstrating some important AR concepts.
At the top it demonstrates how to measure AR. Simply find your ID, and divide it by the WD. In the first row of rings the inner diameter of the rings gets smaller from left to right, while the respective wire diameter (.10″) stays the same. Because of this, the aspect ratio gradually shrinks from left to right. This means that any weave made with these rings would get smaller and tighter as you moved from left to right. Made with the leftmost ring the weave might look too loose, but made with the rightmost ring it might be too tight to even make, while the two middle rings might fall with the ideal AR range and be perfect for the weave. Aspect ratio helps a mailler to make the most aesthetic and practical choice.
Once you have found the ring size that you like for a weave, through the use of aspect ratio you can scale the weave to be larger or smaller. How, you might ask? Because aspect ratio is a ratio, through some simple algebra you can choose a gauge of wire that you would like to make the weave from, and find the inner diameter that you need to achieve the same appearance as in the original ring size. Simply multiply the AR by the WD to find the ID needed to reproduce a ring with that AR in that gauge. In the diagram above you can see that the second row of rings all have the same aspect ratio, yet different wire and inner diameters. This means that weaves made with 19g Swg WD, 5/32″ ID rings will be a scaled, shrunk down version of the same weave made with 12g Swg WD, 2/5″ ID rings. This means that they will have all the same physical properties (except strength), such as flexibility, tightness, and appearance. In summation, any two rings with the same aspect ratio will act the same in a weave, and those close to the same aspect ratio will act close to the same. The opposite also holds true, the greater the difference in aspect ratio, the greater the difference between the same weave made with those rings. In short, choose the aspect ratio that best suits your needs.
Springback and Aspect Ratio:
One very important thing to note when dealing with aspect ratio is springback. Springback is an increase to the inner diameter from the mandrel diameter the wire was wound on that is a result of tension produced by the wire as it is coiled. Metal resists bending to the shape of the mandrel, and as a result, when the tension of coiling is removed, the coil springs away from the center of the mandrel and has a greater inner diameter than the mandrel it was coiled on. As a result of this, you cannot use the mandrel size as the Inner Diameter measurement and expect an accurate aspect ratio, especially with harder metals (except with dead soft metals in which springback is negligible). To get accurate measurements of inner diameter and wire diameter (as there is some variance in thickness in even a single gauge number i.e. 18g SWG could have .048″ or .047″ or .045″) you should use a caliper.
A proper caliper should measure to the thousandth of an inch and have both “ends” like the one above, that allows for both pinching down on wire to find the wire diameter, and spreading out to determine inner diameter, as shown in the pictures below.
Now that you have these up-to-date measurements you can find an accurate aspect ratio of the rings you are using. Springback and actual inner diameter due to springback are important things to note when purchasing pre-made rings or conversing about the aspect ratio of rings.