This pattern creates a collar and cuff for a store-bought sweater.

From the pattern website

Gauge:

The size of the crocheted collar and cuffs for your sweater will vary depending on the sweater you choose to embellish. Although gauge is not important for this project, I have included the measurements of my own sweater. It didn’t leave the thrift store with tags so I don’t know exactly how large it is, but I’m guessing it is a size small. My finished collar is 1 1/2” tall by 13” wide when lying flat. The finished cuffs each measure 5” long, 6” wide at the widest edge and 3 3/4” wide at the narrowest point. The gauge of my work is 4” = 30 sc wide, (14) 3-ch mesh arc stitches wide and 22 mesh arc stitches tall.

Notes:
Any sweater can be modified using this pattern. If you use a fine knit wool sweater you can needle felt the cut edges to prevent fraying. Needle felting is a dry felting process that adheres the fibers of wool together with a sharp barbed tool.