All thumbs

e.g. Marco can't build the model of the atom for the science project. He's all thumbs.

Meaning: awkward and clumsy, especially with the hands

Origin: Human beings and apes have thumbs; most other animals don't. A thumb helps the other fingers pick things up, turn dials, and do other fine motor tasks. But what if all your fingers were thumbs? You'd have a hard time picking up small objects, keyboarding a computer, doing art projects, and so on. That's why this expression means clumsy at doing physical tasks with your hands.

指笨手笨脚。