CO 64 sts, TGCO US4 needles. K 1 rnd. switch to US3 needles, rib 4 rounds. switch to 3.0mm, work to heel. Front and back needles off kilter - 28 sts in front, 36 sts in back. Complete 3 18-row repeats before starting on heel flap. Dec 4 sts on back half of sock before changing to 2.5mm needle for garter st flap. Knit 2.75” (22 ridges) for flap, then work round heel (knit to 1/2 plus 5 sts, dec, etc).

Not sure how it happened, but the foot of one sock is a whole inch longer than the other! I will measure them again after they are washed - socks get pulled this way and that while they are knit, so some settling of the sts is usual.