To assure a lock works perfectly, it needs to be oiled once a year. Locks in more frequent use need to be oiled monthly.
Lock cylinders need to be washed as well and lock oil can be used for thet, too. Spray some oil in the keyhole, insert the key and take it out, wipe the key clean with a soft cloth and repeat until the key stops bringing out dirt. DO NOT turn the key while cleaning with oil.
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