This insertion is in 1918 Priscilla Cotton Knitting, p.6. There are just 6 stitches and 1 pattern row, making this insertion truly reversible.
Priscilla Insert 2 is 0.75 inch wide at gauge.

Skills needed: cast on, slip, knit, YO, k2tog and bind off in knit stitch.

Gauge is not important in this pattern. Any block-able yarn/thread will work. Make a swatch to check gauge and appearance.

10 yards of Aunt Lydia’s Classic 10 thread will make 10 inches of Priscilla Insert 2 at gauge.