Last reviewed: May 2026 - MLC editorial team - UK trade engineering perspective
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Loctite 243 and 271 are the two threadlockers UK engineers should keep on the shelf. Loctite 243 is the medium-strength, hand-tool-removable workhorse; Loctite 271 is the high-strength, heat-required-to-remove permanent threadlocker. Picking the wrong one is the difference between routine servicing and a £200 stripped-stud problem. In workshops across Britain, these products are staples for securing bolts in place without welding or additional hardware. While many applications allow for interchangeability, understanding their specific attributes can save time and money on maintenance costs. For tasks requiring easy removal, Loctite 243 offers flexibility; for permanent assemblies, Loctite 271 provides the necessary strength. Procurement teams must consider these nuances to ensure they are selecting the right product for each job, balancing cost efficiency with operational reliability.
What they have in common
- Both are anaerobic methacrylate adhesives - cure in the absence of air, on contact with metal.
- Both meet ASTM 1782 thread-locking standards.
- Both have a 5-year shelf life from manufacture date.
Header comparison
Where they differ
Strength / break torque
When comparing Loctite 243 and Loctite 271 on strength and break torque for M10 bolts, Loctite 243 offers around 12 Nm of torque, allowing robust hand-tool removal. In contrast, Loctite 271 delivers approximately 32 Nm but necessitates heat application to break free.
| Loctite 243 | ~12 Nm on M10 - robust hand-tool removal |
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| Loctite 271 | ~32 Nm on M10 - requires heat application to break |
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Oily fastener tolerance
Loctite 243 is favoured in UK trade workshops for its tolerance of light oil on fasteners, making it a go-to choice where degreasing isn't practical. In contrast, Loctite 271 demands clean and degreased fasteners, requiring the use of Loctite SF 7063 cleaner to ensure optimal performance.
| Loctite 243 | Tolerates light oil - 'gen-purpose blue' is the go-to for trade workshops where fasteners aren't degreased |
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| Loctite 271 | Requires fastener degreased and clean (Loctite SF 7063 cleaner recommended) |
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Removal method
When comparing Loctite 243 and Loctite 271 on removal method, the standard hand tools suffice for Loctite 243, requiring sufficient applied torque to overcome the cured adhesive. Conversely, Loctite 271 necessitates heating the joint to over 250°C with a blowtorch or induction heater to soften the adhesive before removal with hand tools.
| Loctite 243 | Standard hand tools - sufficient applied torque overcomes the cured adhesive |
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| Loctite 271 | Heat the joint to >250°C with a blowtorch (or induction heater) to soften the cured adhesive, then remove with hand tools |
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Fastener size suitability
In a UK trade workshop, Loctite 243 and Loctite 271 both cover fastener sizes from M6 to M36. However, Loctite 271 is typically reserved for critical structural or safety-related applications involving M10 and larger bolts, setting it apart in demanding scenarios.
| Loctite 243 | M6 to M36 typically |
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| Loctite 271 | M6 to M36 typically, but typically reserved for M10+ on critical structural / safety-related fasteners |
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Cure time (room temperature)
When comparing Loctite 243 and Loctite 271 on cure time at room temperature, the former reaches fixture strength in just ten minutes before fully curing within twenty-four hours. In contrast, Loctite 271 achieves its initial hold after fifteen minutes but also completes full curing in a day.
| Loctite 243 | Fixture time 10 min, full cure 24 hours |
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| Loctite 271 | Fixture time 15 min, full cure 24 hours |
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Typical trade scenarios
In a UK trade workshop, Loctite 243 is favoured for general machinery bolts and bracket fixings due to its flexibility and ease of use, whereas Loctite 271 excels in permanent assemblies like crankshaft pulleys, offering superior vibration resistance and safety-critical performance.
| Loctite 243 | General machinery bolts, bracket fixings, suspension hardware, motor mounts |
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| Loctite 271 | Permanent assemblies, vibration-critical joints, safety-critical fasteners (e.g. crankshaft pulleys, structural bolting) |
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Decision framework: when to pick each
| Scenario | Recommendation |
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| Bolts you might need to remove for servicing | 243 (blue) - always. |
| Permanent assembly / no plan to disassemble | 271 (red). |
| Oily / not degreased fastener | 243 (blue) - only 243 tolerates oil contamination. |
| M8 or smaller fastener | 243 (blue) - 271 on small fasteners makes future removal disproportionately hard. |
| High-vibration application | 243 for routine vibration, 271 for safety-critical (rotating mass, suspension geometry, structural pre-load). |
| Fastener will see >180°C continuous | Neither 243 nor 271 - use Loctite 272 (red, 230°C continuous) or 290 (green, wicking grade, 150°C). |
Real trade scenarios
- Vehicle suspension upper-control-arm bolt: 243 - vibration-resistant, removable for future service.
- Crankshaft pulley bolt (engine rebuild): 271 - permanent, no plan to remove until next rebuild.
- Bracket bolt securing a hydraulic ram: 243 - service-removable.
- Wind turbine main bearing housing: 271 - permanent + safety-critical.
- Set screw on a pulley keyway: 243 - frequent enough access for service.
- Crane pinion gear retaining bolt: 271 with primer for guaranteed cure on heat-treated steel.
Related reference on MLC
Tools + parts for these comparisons (Amazon UK)
Frequently asked questions
What's the difference between Loctite 242 and 243?
242 is medium-strength but requires clean / degreased fasteners. 243 is medium-strength and tolerates light oil. 243 superseded 242 as the standard medium-strength offering - most UK trade workshops only stock 243.
Will Loctite 243 hold an M20 wheel stud?
Yes for routine vibration. For safety-critical (e.g. an aircraft wheel), specify 271 with a primer and document the torque/cure. Wheel stud designs that rely on cone-seat friction don't require threadlocker - check the OEM manual.
Why does Loctite 271 need heat to remove?
The cured anaerobic methacrylate has a glass transition around 250°C. Heating above that softens the matrix and lets hand-tool torque break the bond. Below 250°C, applied break torque exceeds steel-bolt yield and you snap the bolt.
Can I use thread tape (PTFE) instead?
No - PTFE tape is a sealant for pipe threads (BSP, NPT), not a threadlocker. Loctite adhesives create a mechanical bond between the thread surfaces; PTFE creates a soft seal that doesn't resist vibration.
How long does Loctite take to cure?
Fixture (initial set): 10-15 minutes at room temperature. Full strength: 24 hours. At sub-15°C cure time roughly doubles; use Loctite SF 7649 primer to accelerate cure on inactive metals (stainless, zinc-plated).
Will Loctite work on stainless steel?
Yes, but cures slower (stainless is 'inactive' to the anaerobic catalyst). Use Loctite SF 7649 activator/primer to accelerate cure to specification times. Without primer, full cure can take 72+ hours on stainless.
Can I reuse a fastener after Loctite cure?
After 243 removal: yes, clean the threads with a wire brush and re-apply 243 (or 271). After 271 removal: yes, but heat may have annealed the bolt - inspect for damage. For safety-critical assemblies, fit a new fastener.
What does Loctite cost in trade quantities?
50ml bottle of Loctite 243: £15-22 trade. 50ml of 271: £20-28. 250ml bulk bottle for production use: £55-80 (243) or £70-95 (271). RS Components / Brammer / Cromwell are typical UK trade suppliers.
Is Loctite 272 the same as 271?
Similar - 272 is the high-temperature version of 271, rated to 230°C continuous (vs 271's 150°C). Otherwise the same red, high-strength formula. 272 is used for engine internal bolts and exhaust manifold studs.
Can I get Loctite alternatives at lower cost?
Yes - Permabond, Vibra-Tite, Bondloc all offer anaerobic threadlockers with similar performance. Specifying-engineer often prefers Loctite for ISO 9001 / aerospace traceability; for general trade work alternatives are 30-50% cheaper.
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Frequently Asked Questions
What's the difference between Loctite 242 and 243?
242 is medium-strength but requires clean / degreased fasteners. 243 is medium-strength and tolerates light oil. 243 superseded 242 as the standard medium-strength offering — most UK trade workshops only stock 243.
Will Loctite 243 hold an M20 wheel stud?
Yes for routine vibration. For safety-critical (e.g. an aircraft wheel), specify 271 with a primer and document the torque/cure. Wheel stud designs that rely on cone-seat friction don't require threadlocker — check the OEM manual.
Why does Loctite 271 need heat to remove?
The cured anaerobic methacrylate has a glass transition around 250°C. Heating above that softens the matrix and lets hand-tool torque break the bond. Below 250°C, applied break torque exceeds steel-bolt yield and you snap the bolt.
Can I use thread tape (PTFE) instead?
No — PTFE tape is a sealant for pipe threads (BSP, NPT), not a threadlocker. Loctite adhesives create a mechanical bond between the thread surfaces; PTFE creates a soft seal that doesn't resist vibration.
How long does Loctite take to cure?
Fixture (initial set): 10-15 minutes at room temperature. Full strength: 24 hours. At sub-15°C cure time roughly doubles; use Loctite SF 7649 primer to accelerate cure on inactive metals (stainless, zinc-plated).
Will Loctite work on stainless steel?
Yes, but cures slower (stainless is 'inactive' to the anaerobic catalyst). Use Loctite SF 7649 activator/primer to accelerate cure to specification times. Without primer, full cure can take 72+ hours on stainless.
Can I reuse a fastener after Loctite cure?
After 243 removal: yes, clean the threads with a wire brush and re-apply 243 (or 271). After 271 removal: yes, but heat may have annealed the bolt — inspect for damage. For safety-critical assemblies, fit a new fastener.
What does Loctite cost in trade quantities?
50ml bottle of Loctite 243: £15-22 trade. 50ml of 271: £20-28. 250ml bulk bottle for production use: £55-80 (243) or £70-95 (271). RS Components / Brammer / Cromwell are typical UK trade suppliers.
Is Loctite 272 the same as 271?
Similar — 272 is the high-temperature version of 271, rated to 230°C continuous (vs 271's 150°C). Otherwise the same red, high-strength formula. 272 is used for engine internal bolts and exhaust manifold studs.
Can I get Loctite alternatives at lower cost?
Yes — Permabond, Vibra-Tite, Bondloc all offer anaerobic threadlockers with similar performance. Specifying-engineer often prefers Loctite for ISO 9001 / aerospace traceability; for general trade work alternatives are 30-50% cheaper.