The completed square, and below a close-up of the texture.
The third square is made of basket weave texture which is generated by alternating 3 BPTr with 3 FPTr across the square and then reversing the sequence every two rows by working FPTr into the BPTr stitches and vice versa. The turning chains are just 2 on one edge and the other edge is finished with a HTr. Abbreviations are provided in the post for square 1.
Ch 18 with 6 mm, change to 5mm and ch 2 ( = Tch),
Row 1: work Htr in all chains starting with 3rd ch from hook
Row 2 and 3: Ch 2, * work 1 FPTr around each of first 3 HTr, followed by 1 BPTr around each of the next 3 HTr and repeat from * to end of row work a HTr into the Tch to finish the row.
19 sts with 6 relief groups of 3 and a single Htr.
Row 4 and 5: Ch2, * work 1 BPTr around each of first 3 FPTr, followed by 1 FPTr around each of the next 3 BPTr and repeat from * to end of row and work a Htr into the Tch. 18 sts with 6 relief groups of 3 as before with a HT
Row 6 and 7 - repeat row 2 and 3 except you are now working around the posts of post stitches rather than HTrs. It's essentially the reverse of row 4 and 5.
Keep repeating rows 4-7 until 13 rows have been worked and fasten off.
14 rows would have been better but 13 rows keeps the shape an exact square.
This is a lovely thick square and is reversible with texture on both sides.