To screw in is to fasten something by turning a threaded pin. Clockwise, until it stops.
The rule everybody learns is righty-tighty, since almost every thread tightens clockwise. It splits round an object, and screwing in a bulb is the standard example, which is why so many jokes begin with how many people it takes. The opposite is to unscrew. There is a figurative use in screwing up your courage, which comes from tightening rather than fastening.
1phrasescrew inTo fasten something by turning it into a threaded hole.
“Screw in the bulb until it stops turning.”
Practised in A Man Called Ove, Repair & Damage
First appears in chapter 32 of A Man Called Ove.
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