Fixing a Stripped Thread, and the Right Threadlocker

A stripped thread and the wrong threadlocker cause the same kind of frustration from opposite directions — one is a fastener that will not hold, the other is a fastener that will not let go. Both have a correct answer that depends on specifics most people skip past on their way to grabbing whatever is in the drawer.

A note on this guide: this rests on how each repair method restores a thread, not on repairs made here. See how we test.

The thread problem

Why re-threading by force does not work. Forcing a bolt into a thread that is damaged just finishes the job the damage started — cross-threading, or shaving what little good thread remains. The instinct to "just get it started" is exactly backwards here.

Chaser versus insert is a diagnosis, not a preference. A chaser is a cleaning tool: it restores an existing thread that has paint, corrosion or light damage in it, without removing base material. It has nothing to offer a hole where the actual threads are gone — worn smooth, stripped by over-torquing, or snapped off entirely. That situation needs an insert kit: drill the hole to a specified oversize, tap new threads into that larger hole, and install a coiled insert that becomes the fastener's new thread surface. Skipping straight to an insert kit on a thread that only needed cleaning is more work than the job required; trying to chase a thread that is actually stripped will not work at all.

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The threadlocker problem

Threadlocker is not one product with a colour preference — the colours denote genuinely different strength classes, and picking the wrong one has real consequences later. Blue (medium strength) is removable with ordinary hand tools and is the sensible default for anything that gets serviced again — most fasteners on a car fall into this category. Red (high strength) is closer to a permanent bond and typically needs heat to break; it belongs on fasteners that genuinely should not come loose and are not expected to be removed in routine service.

The grades, since colour alone is not what you buy

Colour is a convention rather than a specification, and the number on the bottle is the actual product. The common ones:

The green one is worth knowing about because it does something the others cannot: secure a fastener you have discovered is loose without taking it apart first.

Why it sometimes never sets, which is not a faulty bottle

Threadlockers are anaerobic — they cure in the absence of air and in the presence of active metal ions. Steel supplies those ions readily. Several common materials do not:

Stainless steel, aluminium, zinc-plated and galvanised fasteners, titanium, cadmium, magnesium, black oxide and anodised surfaces are all "inactive" in this sense. On those, cure can be very slow or effectively never happen, and the published strength figures do not apply. Cold helps nothing either — below about 5°C the same problem appears on metals that would normally be fine.

The fix is an activator or primer applied first. If you have ever put blue threadlocker on a stainless fastener, come back the next day and found it still wet, this is why — the product was not defective and you were not using too little.

The mistake to avoid

Using red threadlocker out of habit, or because it was the only bottle in the drawer, on a fastener you will need to remove later. Without heat, that fight usually ends with a rounded socket or a stripped head — turning a five-minute job back into the kind of problem freeing a seized fastener already covers. When in doubt about which fastener you are dealing with, blue is the safer default; save red for the specific cases where the manufacturer actually calls for it.