The 3-needle join is a join used to seamlessly knit together two pieces of fabric. It is similar to a three needle bind off, in that you knit together stitches off of two needles. However, the three needle join leaves you with live stitches, rather than a bound off edge.
How to work a 3-needle join
Set up:Have one-half of the stitches on front needle and the second half of stitches on back needle.
Repeat:Using a third needle, *k2tog the front and back stitch; repeat from * to end.