This cable is called the 3-strand cable but it can also be known as a Braid cable.
Cast On = 29
Finished Size = 6 x 9 inches
Needle Size = 10.5 US
Yards of Yarn = 60-75 yards
Rows = Complete rows 1-12 then 5-12 as needed

The underside is a slip stitch pattern which makes it snug on your arm and very comfortable. It won’t move around. I changed the original pattern to this one because it was the opposite.

It’s an easy pattern for a beginner. There’s the standard type of cable. Even if it’s your first you’ll be ok. I was a beginner when I made all of mine.

In regards to the size. If, for example, you’re making this for someone with a 5 inch wrist then you want the width of the arm warmer to be 1 inch more.

C6F= Slip 3 to the cable needle and hold in front, Knit 3 then knit the 3 stitches on the cable needle.

C6B= Slip 3 to the cable needle and hold in back, Knit 3 then knit the 3 stitches on the cable needle.

There are full assembly and finishing instructions.

The pattern is $2.79 here at Ravelry.

Thanks!!
Heather