I whipped these up yesterday. They’re just a basic crochet tube. Started with 35 ch (or enough to go around your hand across your palm) joined, then dc in ever ch until you’ve crochet about 1.5 inch (or however long you want it up your fingers. I tried mine on throughout the whole process to get it to fit snug). To make a thumb hole, ch 7, skip 7, then continue crocheting in the round until they are as long as you want them. You can leave them like this, but i much preferred the slouchy look. In this case, I made a string of ch 50, and threaded it down each thumb side, drawing it up as I went. Tie it together at the bottom, and wa-la a slouchy pair of arm warmers!
Hope all that made sense. I can’t follow a pattern to save myself let alone write one, but they were truly simple to make!