From the Knit Rowan website:
Drift is a wonderfully soft roving yarn which is knitted on the same needle size range as Big Wool.

This yarn is discontinued. You may find a suitable substituted yarn from the current range.

This item has been discontinued

Details:
Article Number: 9802126
Fibre Content: Merino Wool: 100%
Season: Autumn Winter
Yarn Ball Weight: 100g
Yarn Meterage/Yardage: 80/87
Tension/Gauge Stitches: 7½-9
Tension/Gauge Rows: 10-12½

Recommended Knitting Needles:
Knitting Needle (UK): 000
Knitting Needle (US): 15-19
Knitting Needle, MM: 10 or 15

(These are lightly variegated in very long repeats, so occasionally you will find balls of the same dye lot looking quite different. It is suggested that you use two balls at once and alternate every other row if you would prefer for the colours to blend more evenly.)