Anaerobic threadlockers

Low strength suits small screws under M6 that are removed often. Medium strength suits M6 to M36 bolts removable with hand tools. High strength is for permanent assemblies and needs heating to around 250 degrees C to undo.

It stays liquid in air and cures only when oxygen is excluded between metal threads. Metal ions catalyse the reaction, so on stainless, aluminium or plated parts cure is slower and may need an activator. It is not for plastics, which it can stress-crack.

Clean oil off the thread and apply a few drops where the nut will engage, not at the bolt tip. For blind holes, put the drops at the bottom of the hole so trapped air does not push the compound out. Torque to specification right after applying.

Threadlockers mainly prevent loosening; for pipe threads use a dedicated anaerobic pipe sealant with the viscosity and fillers for taper thread gaps. It can replace PTFE tape on metal threads and leaves no tape shreds in the line. On plastic pipe use a product stated as plastic-compatible.

Apply localised heat to around 250 degrees C to break down the adhesive, then unscrew while hot. Low and medium strength grades can usually be removed with ordinary hand tools. After removal, clean old residue out of the threads before reassembly.

Anaerobic adhesives need active metal ions such as iron or copper to cure, while stainless steel, anodised aluminium and plated surfaces are passive. On these, use an activator primer or a grade less sensitive to the substrate. Low temperature also lengthens cure time.

Liquid grades wick well into pre-assembled threads and suit small sizes. Semi-solid stick grades do not run, which is convenient overhead, upside down or in a toolbox. Both cure by the same anaerobic mechanism.

Yes, oil and grease on the threads lower strength and slow curing. Use a residue-free degreasing solvent and let it dry completely. Some grades tolerate light oil, but cleaning still gives the most consistent result.