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Shake the bottle.
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Mechanically clean the strongly contaminated or rusty fastener.
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By keeping the bottle vertically, spray the fastener. It produces its effect within about 3-5 minutes. In case of multiple screws, spray all of them and start working to ensure more time to produce an effect.
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Knock the screw to make the loosened rust crack and to ease unscrewing.
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In case of heavy rust, repeat the procedure.