How to work an I-cord 3-needle BO
Have an equal number of stitches for each edge to be joined on two needles.
Cast on: Cast on 2 stitches (or desired number) using a third needle. With the WS together, hold the needles with stitches in left hand.
Set Up: Slip the cast on stitches to front (left) needle. K2 off front needle, k2tog-tbl from front and back needle.
Repeat: *Slip 3 stitches from right needle to front left needle. K2, put needle into back leg of next 2 stitches on front needle and first stitch on back needle and k3tog-b.
Rep from * until all stitches have been bound off.