No particular gauge or hook size is necessary. I used a size I, with worsted weight yarn, and I crochet fairly loosely.
xxxtrc (fully extended trc)
To make xxxtrc, yarn over twice and pull up a loop, [yarn over and draw through one
loop, yarn over and draw through two loops] three times. If you prefer, you can use a tr tr instead (yarn over four times and work the loops off two at a time). I like the extended stitches because they seem more sturdy and I don’t get that long, dangly single strand of yarn left at the top of the stitch. (It’s probably just me! LOL!)
Row 1: Sc in 2nd chain from hook, and in each chain, (34 sts)
Row 2: [Sc in first 2 sc, ch 2, skip next 2 sc] across.
Row 3: [Sc in first 2 sc, 2 sc in ch-2 space] across.
Row 4: Slip st in first 2 sc, ch 6 (serves as first xxxtr). Working behind, insert hook into first slip st to make a xxxtr. [Skip next sc, xxxtr in next sc, work behind to make another xxxtr] across. (17 Xs made)
Row 5: Sc across (34 sts)
Repeat rows 2-5 four more times.
With preferred right side facing (I use the back of the extended stitches as the right side. For a flatter appearance, use the front of the stitches as the right side), work a sc border as follows:
Sc in each stitch across top and bottom.
1 sc in the end of each sc row, 2 sc top half of ‘X’ and bottom half of ‘X’ (a total of 4 sc worked into sides of each row of X’s).
Corners: Sc, ch1 sc.
At end of first border round, sl st into first sc, ch1, turn. Working in opposite direction, sc in each stitch around, working 3 sc in each corner.