This pattern has two possible versions. I made one with #5 bulky yarn and another one using #4 medium worsted yarn.

US J-10/6.00mm
US K-10.5/6.50 mm
Red heart soft essential stripes, 4 oz, 113g, 110 yd, 101 m, approx 3 skeins
Yarn Weight 5 - Bulky
Also known as chunky weight. These CYC #5 yarns work up to a recommended gauge of 12-15 stitches over 4 inches in knitting and 8-11 stitches over 4 inches in single crochet.
https://yarnsub.com/yarns/red_heart/soft_essentials_stripes
Worsted yarn, big twist value, 380 yd, 6 oz, 347m, 170g

Stitches
HDC3tog= yarn over and insert hook in just completed stitch, pull up a loop, yo and insert hook in next stitch, pull up a loop, yo, hook into next stitch, pull up a loop, yo and pull through all 7 loops. CH1 to close.
CH 1 and/or CH 2 before first stitch of a row does not count as a stitch.

Gauge
Big twist yarn, J 6mm hook=
11 DC x 5 rows=4”

Bulky Scarf= approx 68”x 7”
Worsted scarf= 68” x 6 1/2”