Overview
Loctite® Grade AA is a high-strength anaerobic threadlocker from Henkel’s classic letter-grade family, formulated for the permanent locking and sealing of threaded metal fasteners. It cures in the absence of air between close-fitting metal surfaces, turning into a tough, thermoset plastic that completely fills the thread gap.
Once cured, Loctite Grade AA:
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Prevents loosening from shock, impact and continuous vibration
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Seals the helical path against fluids and gases, helping to reduce leaks
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Shields engaged threads from rust, fretting and galling over long service
It is especially useful where older drawings, aerospace/defense documents or plant standards still specify “Loctite Grade AA” rather than a modern numeric product code.
Why choose Loctite Grade AA?
1) Permanent-strength retention
Grade AA is positioned as a high-strength threadlocker: fasteners are effectively fixed for the life of the assembly. Disassembly of larger bolts, if ever required, normally demands substantial torque and often localized heating of the joint.
2) Compatible with spec-based designs
Many legacy programs and controlled industries still reference letter grades (AA, A, B, C, etc.). Using Loctite Grade AA makes it easier to match existing approvals, drawings and qualification records, especially in aerospace, defense and older industrial designs.
3) Locks and seals in one operation
Because it fills the clearance between male and female threads, Grade AA locks the fastener against loosening and seals the thread path in a single step. This can reduce or replace mechanical lock devices (spring washers, lock nuts) and separate thread sealants.
4) Reliable anaerobic curing
Loctite Grade AA is a single-component liquid that cures at room temperature. No mixing, no separate hardener—simply apply, assemble the joint and allow it to cure in place.
5) Versatile for bolts, nuts and studs
The product is well suited to common machinery bolts, nuts and studs, from fine threads through to typical medium sizes, in pumps, gearboxes, frames and precision assemblies that must not come loose.
Typical Applications
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Critical bolts and studs in pumps, motors, gearboxes and compressors
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Fasteners subject to high vibration and shock in industrial machinery
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Aerospace/defense or legacy equipment where “Loctite Grade AA” appears in the specification
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Threaded joints that must be locked and sealed for the life of the assembly
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Retrofitting or repairing older machines originally assembled with letter-grade products
Loctite Grade AA is intended for metal-to-metal threaded fasteners and is not recommended for plastic threads or oxygen/strong oxidizer systems.
How to Use Loctite Grade AA
Step 1 – Surface preparation
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Remove loose rust, dirt and old threadlocker from male and female threads.
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Wipe off heavy grease, thick oil and anti-seize.
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Light “as-received” oil films may be tolerated, but for critical joints, cleaner metal gives more predictable strength and sealing.
Step 2 – Product application
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Shake the bottle briefly before use.
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Apply a continuous bead of Loctite Grade AA along the male threads, covering the full area that will be engaged.
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For blind holes, apply a small amount into the female threads so that the adhesive is driven through the engagement as the fastener is installed.
Step 3 – Assembly and tightening
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Assemble the joint promptly after application.
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Tighten the fastener to the specified torque.
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Avoid repeatedly loosening and retightening once the adhesive has started to fixture, as this can disturb the bond line.
Step 4 – Cure and return to service
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Allow the assembly to remain undisturbed until it reaches handling strength.
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For maximum performance, especially on passive metals or in demanding service, allow up to 24 hours at room temperature before applying full load, pressure or high vibration.
Step 5 – Disassembly (if ever required)
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It is a high-strength permanent grade.
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Disassembly of larger fasteners often requires:
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Localized heating of the fastener area (only if compatible with your base materials and design) to soften the cured adhesive, and
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High torque with appropriate tools to break the bond while the joint is still hot.
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Safety & Handling
As with most anaerobic threadlockers, typical safety considerations for Loctite Grade AA include:
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May cause eye and skin irritation on contact
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Repeated or prolonged skin contact may cause sensitization in susceptible individuals
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Vapours or mists can cause mild respiratory irritation in poorly ventilated areas
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Uncured product may be harmful to aquatic life if released uncontrolled
Good practice guidelines
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Use in well-ventilated areas.
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Avoid contact with skin and eyes; wear safety glasses and suitable protective gloves.
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Wash hands thoroughly after handling and before eating or drinking.
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Do not dispose of uncured product into drains or natural waterways.
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Store in the original, tightly closed container, in a cool, dry place away from heat, sparks and direct sunlight.
Always consult the latest Safety Data Sheet (SDS) for Loctite Grade AA applicable to your country or region.
FAQs
Q1: What is Loctite Grade AA used for?
Loctite Grade AA is used as a high-strength threadlocker to permanently lock and seal metal fasteners in critical equipment. It is often specified on legacy drawings and standards that refer to letter-grade products instead of modern numeric codes.
Q2: How is Grade AA different from Grade A, Grade B or Grade C?
Within the letter-grade family, Grade AA is positioned as a high-strength, general-purpose anaerobic threadlocker used where permanent locking is desired and a specific AA designation appears in the spec. Grade A and Grade C are other letter-grade variants tuned for different viscosities and strength profiles; they’re typically chosen when those exact grades are called out.
Q3: Is Loctite Grade AA removable?
Loctite Grade AA is considered a permanent threadlocker for most practical purposes. Small fasteners may be removed with strong hand tools, but larger fasteners usually require localized heating and high torque for safe disassembly.
Q4: What fastener sizes are suitable for Loctite Grade AA?
Grade AA is typically used on small to medium/large bolts, nuts and studs in machinery, structures and equipment. For tiny, delicate screws, a low-strength grade is usually safer; for very large studs with wide clearances, a higher-viscosity heavy-duty product may be preferred.
Q5: Can I use Loctite Grade AA on stainless steel or plated fasteners?
Yes, Loctite Grade AA can be used on many common metals, including stainless and plated fasteners. Cure speed may be slower on “passive” metals, so allow adequate time before fully loading the joint, or consider an activator if rapid strength build-up is critical.
Q6: Is Loctite Grade AA oil-tolerant?
Like most anaerobic threadlockers, Grade AA works best on clean metal. It may cope with light oil films, but heavy oil, grease or anti-seize should be removed to ensure consistent strength and sealing performance, particularly in safety-critical applications.
Q7: Can I use Loctite Grade AA on plastic threads or in plastic housings?
No. Anaerobic threadlockers such as Grade AA are formulated for metal-to-metal threads and can cause stress cracking in some plastics. They also do not cure properly on non-metallic surfaces. For plastic or mixed metal/plastic joints, a plastic-compatible adhesive should be used.
Q8: Does Loctite Grade AA also seal against leaks, or only lock threads?
Loctite Grade AA both locks and seals threaded joints. By filling the gap between male and female threads, it helps prevent the passage of fluids and gases along the thread helix and improves corrosion resistance. It does not replace flange gaskets on mating faces, but it is very effective at sealing through-thread leak paths.
