More on Screw Loose from Infoplease:

• Screw Loose - Screw Loose (A). Something amiss. The allusion is to joinery kept together by screws. Source: ...
• screw: meaning and definitions - screw: Definition and Pronunciation
• Leglin-girth - Leglin-girth To cast a leglin-girth. To have “a screw loose;” to have made a faux pas; ...
• Dictionary of Phrase and Fable: S - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "S"