Over a multiple of 4 sts plus 3 edge sts, cast on to desired width.
Row 1 (right side): K1 (edge st), * T2R, then T2L *, repeat from * to * ending with K1 (edge st).
Rows 2 and 4: P across.
Row 3: K1 (edge st), * T2L, T2R *, repeat from * to * ending with K1 (edge st).
Repeat rows 1 to 4 until desired length.