This decorative stitch is the incorporation of zig zag chain stitch and cable chain stitch. It looks more like a cable chain stitch in zig zag pattern. It follows two parallel stitch lines.

I will be working on a slightly curved parallel stitch lines. You need to know the chain stitch and cable stitch to be able to do this stitch.  

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Fig 1: With the base on one of the stitch lines, make a loop as we would in a chain stitch. Place the needle at about 90 degrees angle near the broader end of the loop and wrap the thread around as shown.   Fig 2: With the thread still wrapped, put the needle in through the other stitch line and bring it out on the first stitch line at 90 degrees angle. Loop the thread around the needle from inside out.

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Fig 3: When you pull out the needle to tighten the loop, we would get two zig zag loops connected by a small cable.      Fig 4: Continue with this action. Always remember to keep the needle at the broader base of the previous loop.

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Fig 5: Keep the needle at always about a 90 degrees angle to get a perfect zig zag pattern.   Fig 6: And, always loop the thread around from inside out. When your needle is directed towards left side, the loop will be from left to right and vice versa.

zig_zag_cable_chain_stitch_7 Fig 7: A completed zig zag cable chain pattern will show like this.