Multiple of 4 stitches, 2 row repeat.
Modified heel flap by jbatch for Porthos socks by Caoua Coffee.
The modification for the heel flap is the alternating sl yb/sl yf on the RS rows (the original pattern keeps the yarn in back at all sl sts).
This is also variation on the Double Woven Rib Stitch (as found on page 95 in 'A Treasury of Knitting Patterns' by Barbara G. Walkers or at Knittingfool.com), the difference is an …
Multiple of 4 stitches, 2 row repeat.
Modified heel flap by jbatch for Porthos socks by Caoua Coffee.
The modification for the heel flap is the alternating sl yb/sl yf on the RS rows (the original pattern keeps the yarn in back at all sl sts).
This is also variation on the Double Woven Rib Stitch (as found on page 95 in 'A Treasury of Knitting Patterns' by Barbara G. Walkers or at Knittingfool.com), the difference is an alternating sl1 instead of sl 2 on the RS and knitting in pattern instead of purl all on the WS.

Shown with a cast-on count of 30 stitches.