1
general::
Physically awkward, especially with respect to the hands, as in When it comes to knitting, Mary is all thumbs. The notion of this idiom derives from a proverb in John Heywood's collection of 1546: "When he should get aught, each finger is a thumb."
American Heritage Idioms
2
general::
Phrase(s): all thumbs
Fig. very awkward and clumsy, especially with one’s hands. • Poor Bob can’t play the piano at all. He’s all thumbs. • Mary is all thumbs when it comes to gardening.
McGrawhill's American Idioms And Phrasal Verbs