How to: work the three-needle cast off
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With this technique you cast off two pieces and join them at the same time, making it a neat and time-saving way to join shoulder seams rather than spending time casting off and then sewing up. This cast off leaves a relatively low ridge that some patterns use as a decorative touch when placed on the right side.
What is so satisfying about this technique is that you get a strong seam with aligned columns of stitches. To keep the low profile cast-off ridge on the purl side of two stocking stitch pieces, place the knit sides together, and vice versa for the ridge on the knit side.
Hold the two needles holding the stitches to be cast off parallel and in your left hand, with matching sides together, and if using the working yarn from one of the pieces, make sure this is coming from the back needle.
Using a third needle of the same size in your right hand, insert this needle into the back of the first stitch on the front needle and through the front of the loop of first stitch on the back needle, in effect picking up the two inner legs of the stitches. Knit the two stitches together (k2tog) and slip them off the left-hand needle, leaving one stitch on the right-hand needle.
Repeat for next stitch of both needles, knitting them together through front and back sts and off the left needle. With two stitches on the right-hand needle you can now cast off a stitch in the usual way, with one of the needles in your left hand lifting one stitch over the other and off the right-hand needle. This leaves one stitch on the right-hand needle.
Continue along the row, knitting the first two stitches together then using the left needle to cast off a stitch. At the end of the row, fasten off the last stitch in the usual way, by cutting the yarn and pulling through.
Be sure to weave in any yarn tails at either end of the ridge securely, especially if a shoulder seam that carries the weight of the garment and possibly also a sleeve.
Should you have to unpick the cast off for any reason, you’ll find one piece will have a cast off edge, while the other will have live stitches.