This is a very elastic cast on that provides a looped bottom edge.
In the sample pictured, the cast on row (considered the Right Side) was followed by a knit row which created the purl bumps directly above the cast on row on the Right Side. When followed by stocking stitch as in this sample, the cast on will flare the knitted fabric at the cast on edge a little, but not as much as the Crossed Yarn Over LTCO.
This cast on begins just like a regular Long Tail Cast on:
~ Bring the yarn tail between the index and middle finger
~ In front of the thumb
~ Around the back of the thumb and over the yarn coming from the index finger
For the Double Thumb Loop Cast On:
~ Wrap the thumb yarn one more time around the thumb
The thumb yarn lies on top of the yarn coming from the index finger
~ Insert the needle from the bottom through both thumb loops
~ Scoop the yarn coming from the Index finger
~ Bring the yarn through both thumb loops
~ Snug up both loops
Start this cast on with just a twisted stitch.
If you start with a cast-on stitch, there will be 2 horizontal threads under the cast on stitch -- not very nice :(
Starting with just a twisted stitch will give a nice smooth cast one edge.
Using this cast on with "fuzzy" yarn can be a bit of a challenge when you are trying to snug up the double thumb loops. Slippery yarns only require a tug on the tail end of the yarn to close the double loop up but wool may require a little tug on the top loop to help feed the yarn from the bottom loop through.