This post is from a comment I made on the Beading Daily site HERE.

**Buying Jump Rings with Outer Diameter-RISKY**

Unfortunately, many (most?) packaged jump rings found at craft stores only provide the outer diameter (OD). If the package of rings doesn’t say “inner diameter” or “ID,” then you’re probably looking at the outer diameter.

For example, I was at a “hobby” store this week and was looking at packaged rings. The packages only said “6mm” — not inner diameter and no wire gauge! Worthless to me.

If you’re using a really simple chain maille pattern that results in really loose weave, this might not be a problem. However, for more complex weaves with dense patterns, this can be a big problem. Use rings with inner diameters too big, and the chain will look sloppy. Use rings with inner diameters too small, and the chain may be too stiff, assuming you can make the chain at all!

**From Outer Diameter to Inner Diameter**

Fortunately, if you know the wire gauge, you can easily figure out the inner diameter.

**Inner diameter = outer diameter – (gauge x 2)
OR
ID = OD – (ga x 2)**

For example, 20 gauge wire is 0.81 mm thick. If the outer diameter is 6 mm, you subtract the gauge TWICE (once for each side of the ring) to get the inner diameter:

**6 mm – (0.81 x 2) = 6 mm – 1.62 = 4.38 mm inner diameter.**

Make sure to use the millimeters for the gauge, not the gauge number! Example: Use 0.81 mm, not 20.

**From Inner Diameter to Aspect Ratio**

Now, with the inner diameter (ID), you can figure out whether the rings will work for your weave! You will be able to determine the aspect ratio (AR), which is the MOST IMPORTANT NUMBER to know when making chain maille.

**AR = ID / gauge**

Using the same example rings above (20 ga, 4.38 ID), we get this AR:

**AR = 4.38 / 0.81 = 5.4 AR**

Here are some other common wire gauges (AWG) and millimeter equivalences.

16 ga = 1.29 mm

18 ga = 1.02 mm

20 ga = 0.81 mm

22 ga = 0.64 mm

**Example ID and AR from 6 mm Outer Diameter Rings**

Now, if we use the same 6 mm outer diameter rings as an example, we can see what ID and ARs will result from different wire gauges. Again, OD = outer diameter, ID = inner diameter, AR = aspect ratio.

16 ga wire (1.29 mm thick)

ID: 6 mm OD – 2.58 = 3.42 ID

AR: 3.42 mm / 1.29 = 1.8 AR (good luck making anything with an AR this small!)

18 ga wire (1.02 mm thick)

ID: 6 mm OD – 2.04 = 3.96 ID

AR: 3.96 mm / 1.02 = 3.88 AR

20 ga (0.81 mm thick)

See examples above

22 ga (0.64 mm thick)

ID: 6 mm OD – 1.28 = 4.72 ID

AR: 4.72 mm / 0.64 = 7.38 AR

So, what does all this mean? What it means is you need to know the measurements of the rings to know if they will work for your chain. Before you buy those rings, do the math! Otherwise, you may waste your money and be disappointed with the results.

## A Practical Example

**Suggested rings:** Let’s say you’re looking at instructions for some chain maille pattern. The instructions might say use 18 ga wire with 4.5 ID. Ok, now you know how to figure out the inner diameter if the packaged rings only have the OD.

**AR of suggested rings:** Maybe that 18 ga wire seems too thick and you want to use 20 ga wire because it is more petite. Ok, first you find the AR of the suggested rings.

**4.5 ID / 1.02 = 4.4 AR**

Thus, the AR of the suggested rings is 4.4, but remember, you want to use a smaller gauge, so you need to adjust the ring size.

**Finding the ID with smaller gauge wire:** Since AR = ID / gauge, then AR x ga = ID. Using this formula, you find that with an AR of 4.4 and 20 gauge wire (0.81 mm, remember?), you need an inner diameter of 3.56 mm.

**AR x ga = ID 4.4 x 0.81 mm = 3.56 mm**

Ok, you’re not going to find pre-made rings with 3.56 ID, but you will find rings with 3.5 ID, and that’s close enough. Your weave will be ever-so-slightly tighter than a weave made with the suggested rings (AR = 4.32). If you find rings with an 3.6 ID, that will be even better, though just a hair looser than using the suggested rings (3.6 / 0.81 = 4.44 AR).

4.5 ID, 1.02 gauge, 4.41 AR (suggested by the instructions)

3.5 ID, 0.81 gauge, 4.32 AR (very slightly tighter)

3.6 ID, 0.81 gauge, 4.44 AR (very slightly looser)

**The result:** So here you are now: you have your 20 gauge rings with 3.5 mm ID, and you make your bracelet following the instructions. Even though you’re using different wire gauge and ID than specified in the instructions, your bracelet will be as beautiful as the one in the instructions! All the proportions are the same, just scaled down.

## Skip the Math

Confused by the math? I got tired of doing all the math, so I made an Excel spreadsheet (calculator) to do it all for me. You can see and download it here: https://chainofbeauty.wordpress.com/chainmaille-resources/

Ok, I know this is a long and complicated discussion of store-bought rings, but I hope it helps everyone get the right rings so that their chain maille projects will be fun and will result in beautiful chain maille jewelry!

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