Lithium waterproof grease
How to lubricate entry doors and what to use : Lithium Waterproof Grease
Quote from Article entitled How to lubricate entry doors and what to use:
It is not recommended to use ordinary lubricants for this type of locking-mechanisms, as the lock may get jammed, when the substance dries up. In this case, it's better to use dag (in other words, graphite dust) as a lubricant. You can get it by milling the core of an ordinary pencil, but is there any use? Every specialized store sells a good graphite lubricant in a spray can. It reduces friction between moving surfaces, protects from dust, and prevents parts from corrosion. Silicone aerosol is also very effective for oiling such type of locks: due to its capacity to repel moisture, the aerosol provides smooth sliding, and protects the metal from corrosion (NB: it is better to overspay the aerosol with a little tube).
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