Classic wool/nylon sock yarn by Lang Yarns: 50g ball (= 210m) with heel strengthening in more than 60 plain and marled shades!
Great for combining, contrasting and colourwork.
A little spool of matching heel/toe strengthening is inside each skein, this can be knitted in with the sock wool at points where the wear is greatest to ensure that your handmade socks stay in tip top condition for longer.