These fingerless mittens are knitted in the round on a set of double-pointed needles.
For the mittens shown in the pictures I used Regia World College sock yarn in DK. Very cleverly a 150g ball creates 3 almost perfectly matching pairs of gloves.
But any other DK yarn should be fine.

The size fits a medium-sized adult hand.
Adjustments can easily be made. For example you can make the cuffs longer or shorter, or widen the gloves my adding 4sts to the width. (Be aware that this may affect the amount of yarn needed)