Yarn listed is knit double stranded.
The needle size will depend on the yarn you are using. Yarn can be anything from your stash heavy enough for slippers. I used worsted weight and US size 9 circular needle, eliminating the back seam.
Please note: the pattern lacks instructions for assembly, and is a one size only pattern.
No longer available at original source, but is available from the Wayback Machine, linked above.