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screw
key (of a clock, watch, etc.); spring
ドライバーで捻子を締めてください。
Please tighten the screw with a screwdriver.
棚を組み立てるのに捻子が必要だ。
I need screws to assemble the shelf.
捻子がなくなったので買いに行った。
I went to buy screws because I ran out.