Double yarn overs can be used for shaping or decoration. They create a large hole that is at least two times larger than a normal eyelet made with a single yarn over. In essence, a double yarn over is worked by wrapping the yarn twice around the needle and then working each wrap as a separate stitch on the following row. For this tutorial I will be pairing the double yarn over (that creates two stitches) with two decreases to keep the stitch count the same. When using a double yarn over for shaping, keep in mind that each one creates two stitches at once.
How to Work It
When your double yarn over is needed in the pattern, wrap the yarn around the needle twice. As you can see, there are two wraps of yarn around the left needle. If your yarn overs wrap in a different direction (all knitters knit differently) do not despair; wrap whichever way is most comfortable for you as it can be easily sorted on the following step.
Working across the wrong side, work your pattern as established (this happens to be on a stockinette background, so I am working purl stitches) to the double wrap.
We will work the first wrap of the double yarn over as a purl stitch and the second wrap as a knit stitch. This is just a general rule to follow: If the pattern being used states to knit the first stitch and purl the second by all means work the pattern as directed. Insert the right needle purlwise into the large hole created by the first wrap. You want the hole to appear large and open at all times when working this technique.
Wrap the yarn purlwise and pull through. There is one new stitch created on the right needle, and the left needle is still inserted into the large eyelet awaiting the second stitch.
Bring the right needle in front of the work and insert knitwise into the remaining wrap.
Wrap the yarn.
Pull the second stitch through. As you can see, the top of the large eyelet created by the double yarn over has a lovely twisted look where the active yarn has been twisted around the double loop to create two stitches.
I worked two more rows in stockinette stitch, and as you can see, the double yarn overs create a larger hole in the work than just a regular eyelet.