Anaerobic sealers cure when there is no oxygen present.

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Anaerobic sealers cure only when oxygen is not present. Their chemistry relies on a redox-initiated polymerization that proceeds when the liquid is confined between closely fitting metal surfaces and air can’t reach it. In the presence of oxygen, the reaction is inhibited, so the material stays liquid. When parts are assembled and the gap excludes air, curing occurs, forming a solid seal. Moisture and light aren’t the drivers for this cure, unlike some other sealants that require moisture or ultraviolet light.