Trades and renovation

The list for a job somebody is paying for. In it is l’écrou, the nut that goes on a bolt, and it is the same word as English « screw » — with the halves swapped. Old French escroue came from Latin scrofa, the sow: the threaded hole was named after the animal, on a resemblance the Romans evidently found obvious and nobody since has wanted explained. English borrowed that word and gave it to the *male* part, the screw you turn; French kept it for the *female* part, the nut you turn it into, and calls the screw la vis. So the two languages hold one word and each points it at the opposite piece of the same pair, which is why serrer l’écrou is « tighten the nut » and never « tighten the screw ». English « nut » is a different metaphor entirely, and a later one.