this is very adjustable, not specific

WOOL (I’ve been using Patons worsted/knit loosely/#8 16 inch cable: so easy - CO 33 because when I knit in the round I slip the first stitch from R needle to the L needle in order to K2tog to avoid the gap, so actually knitting 32 round & round for about 5 inches. Then do a loose button hole (BO 5, then k around to where you BO the row before & CO 5) then knit 4 more rounds (forming the loop for the carabiner). Then at the beginning of the buttonhole, BO 17. Right after BO those 17, you’ll be on the first row of the flap, purl that row. I’m not sure it makes any difference but I did that thinking it helps the flap fold over a bit neater. Kind-of like scoring card stock to make a fold. Then do the rest of the flap stockinette for almost 4 inches, then K 4 rows and BO. I did K4 at the beginning & end of each row; then BO for some but once felted couldn’t see much difference, so do what you want. Turn inside out, whip stitch the bottom, aligning it so the loop is on the side, turn back to the right side, then felt.
add magnetic closures, sew or glue button on outside of flap to hide the metal closure, add carabiner to loop (so far the best place for a variety of colors & inexpensive is Home Depot). Easily vary size, do stripes, could needle felt embellishments…

unfelted about 5 inches wide, 7 high results in finished about 3 wide, 5 high