Loctite 243 Medium Strength Thread Locker Blue

Medium Strength ·

Anaerobic Curing ·

Medium Viscosity ·

Acrylic Ester

Threadlocker

Oil Tolerant ·

Hand Removable ·

For Locking and Sealing All Metal Threaded Fasteners

Module 1: Core Technical Overview 

Core Process Conclusion

LOCTITE® 243™ is not an ordinary threadlocker, but a medium-strength anaerobic locking solution engineered for threaded fasteners requiring regular disassembly. Its advantages of oil tolerance, broad substrate compatibility and thixotropy enable it to simultaneously achieve thread locking, sealing against leakage and post-maintenance in mechanical manufacturing, automotive, equipment operation and maintenance scenarios, adapting to thread assembly under various working conditions.

Module 2: Technical Data Matrix & Performance Curves

Key Curing & Mechanical Properties 

Performance Curve Insights

📈 Curing Speed vs Substrate/Temperature/Clearance

TDS data shows: At 23°C, curing speed is the fastest for M10 bolts on steel substrates, and slightly slower on inert substrates such as stainless steel; elevated temperature significantly accelerates curing speed, and curing speed decreases with larger clearances – the curing speed at 0.25mm clearance is about 40% lower than that at 0.05mm clearance.

Selection Insight: For high-speed production lines or inert substrates (stainless steel, galvanized parts), it is recommended to match with LOCTITE activators (7471™, 7649™, etc.), which can reduce curing time by more than 50%; when thread clearance exceeds 0.15mm, increase the application amount and extend curing time to ensure locking strength.

📌 Environmental Resistance Insight

This product maintains 115% strength retention after 5000 hours of immersion in 125°C engine oil; 80% strength retention after 5000 hours of immersion in 23°C acetone, meeting the chemical and temperature requirements of most industrial working conditions.

Selection Insight: Directly applicable to scenarios in contact with engine oil and brake fluid such as automotive and construction machinery; for contact with strong oxidizing media (e.g., chlorine gas) or pure oxygen environments, replace with LOCTITE special anti-oxidation series threadlockers.

Module 3: Application Scenarios & Substrate Compatibility

Typical Threadlocking Applications

Substrate Compatibility Recommendations

Process Tip: For all metal substrate bonding, if the surface is heavily contaminated with oil, degreasing with LOCTITE cleaning solvent is recommended; for inert metal substrates requiring rapid curing, prioritize matching with LOCTITE 7471™ and other activators for significant improvement in curing efficiency.

Module 4: Process Engineering Solutions

💰 Core Insights for Cost Reduction & Efficiency Improvement

1.       Simplify pre-treatment process: Utilize the product's oil tolerance property, no thorough degreasing needed for slightly oil-contaminated surfaces, saving degreasing solvent costs and pre-treatment time, reducing pre-treatment man-hours by 30% for a single production line.

2.       Precise control of application amount: No excessive application required for threadlocking – 3-5 drops per fastener for M6-M16 bolts is sufficient. Excessive application will prolong curing time and cause material waste; precise control can reduce glue consumption by 25%.

3.       On-demand use of activators: Activators are only required for inert substrates (stainless steel, galvanized parts) or low-temperature working conditions, no addition needed for active metal substrates, reducing activator procurement costs and avoiding unnecessary material consumption.

⚙️ Validated Automated/Manual Application Parameters

🧪 Curing Process Optimization Strategies

•         Temperature optimization: Curing speed decreases significantly when ambient temperature is below 15°C; preheat workpieces to 23–30°C to shorten curing time and ensure locking strength; for high-temperature environments (＞40°C), accelerate assembly speed after application to avoid premature curing of glue.

•         Clearance control: The optimal thread clearance is 0.05–0.15mm; for larger clearances, increase application amount and match with activators; for smaller clearances, appropriately reduce application amount to avoid incomplete curing.

•         Activator usage skills: When using activators, apply evenly on thread surfaces, air dry for 1–2 minutes before gluing to avoid glue failure caused by excessive activators; the amount of activator is sufficient to cover the thread surface.

📦 Storage & Mass Production Management Tips

•         Optimal storage: Store in a dry and dark place at 8–21°C, strictly prohibit exposure to high temperature (＞28°C) or direct sunlight, otherwise it will cause premature curing, viscosity increase and affect usage effect.

•         Production line management: Unopened products have a 12-month shelf life; it is recommended to use up opened products within 30 days, do not pour unused glue back into the original bottle to avoid contamination; clean dispensing tools regularly to prevent glue curing and needle blockage.

•         Mass production control: In mass production, use the product's UV fluorescent property to inspect complete application with UV lamps, reducing defective products; it is recommended to let stand for 24 hours after curing before subsequent processing to ensure optimal strength.

Module 5: Compliance & Certification

•         Test standard compliance: All mechanical and curing performance data are tested in accordance with international standards such as ISO 10964 (thread torque test), ISO 10123 (shear strength test), ISO 11359-2 (glass transition temperature test), with true and reliable data.

•         LMS batch number traceability: Each batch of products complies with Henkel LOCTITE® Material Specification (LMS), can provide batch quality control test reports, supports full product link traceability, and ensures mass production quality consistency.

•         RoHS / REACH compliance: Complies with the current EU and US Restriction of Hazardous Substances directives, free of hazardous substances, can provide the latest SDS (Safety Data Sheet) compliance statement, adapting to various global compliance production needs.

•         Safety compliance tip: Operate the product in accordance with SDS requirements, avoid direct skin contact, and it is recommended to wear protective gloves during operation; strictly prohibit use in pure oxygen, oxygen-enriched environments and strong oxidizing medium sealing scenarios.

•         Quality control: Each batch of products undergoes strict quality inspection before leaving the factory to ensure that key parameters such as viscosity, curing speed and locking strength meet standards, and unqualified products are strictly prohibited from leaving the factory.

Module 6: Expert FAQ

Q1: Why is LOCTITE 243 suitable for threaded scenarios requiring disassembly, and what is the difference from high-strength threadlockers?

A: LOCTITE 243 is a medium-strength threadlocker, removable with standard hand tools after curing, balancing locking reliability and post-maintenance convenience; high-strength threadlockers (e.g., LOCTITE 271) require heating for disassembly after curing, suitable for permanent locking scenarios without disassembly. The core advantage of LOCTITE 243 is "removable and reliable", adapting to equipment threads requiring regular maintenance.

Q2: Why is the curing speed slow or even no curing after applying LOCTITE 243? How to solve it?

A: There are 3 main reasons: ① The substrate is inert metals such as stainless steel and galvanized parts, with inherently slow curing speed; ② Excessively large thread clearance (＞0.25mm), air cannot be completely discharged; ③ Too low ambient temperature (＜15°C). Solutions: ① Match with LOCTITE 7471™ and other activators; ② Control thread clearance at 0.05–0.15mm and increase application amount; ③ Raise ambient temperature to about 23°C or preheat workpieces.

Q3: What media can LOCTITE 243 withstand, and can it be used in high-temperature and oil-contaminated scenarios such as automotive engines?

A: It can withstand common industrial media such as engine oil, unleaded gasoline, brake fluid, ethylene glycol aqueous solution and ethanol, with 115% strength retention after 5000 hours of immersion in 125°C engine oil, fully adapting to high-temperature and oil-contaminated scenarios such as automotive engines and gearboxes; strictly prohibit use in contact with strong oxidizing media such as chlorine gas and pure oxygen environments.

Q4: If the thread surface is oily, is thorough cleaning required before using LOCTITE 243?

A: No thorough cleaning is needed. LOCTITE 243 has excellent oil tolerance performance and can withstand slight surface contamination from cutting oil, lubricating oil, rust-preventive oil, etc.; however, if the oil contamination is severe (oil film thickness ＞0.1mm), degreasing with LOCTITE cleaning solvent is recommended to avoid affecting curing effect and locking strength.

Q5: Can LOCTITE 243 be used for plastic threads, and will it cause plastic cracking?

A: Not recommended for regular use on plastic threads, especially thermoplastics (e.g., PC, ABS). LOCTITE 243 generates slight internal stress during curing, which may cause plastic stress cracking; if it is really necessary to use on plastic threads, a small-batch compatibility test is required in advance, and use only after confirming no cracking; prioritize the use of LOCTITE plastic-specific threadlockers.

Q6: How to clean the cured LOCTITE 243 adhesive layer, and how to remove thread residues after disassembly?

A: The cured adhesive layer can be cleaned in two ways: ① Mechanical grinding (e.g., sandpaper, steel wire brush), suitable for thread residues on large parts; ② Soak with LOCTITE special solvent and then wipe, suitable for precision threads; for thread residues after disassembly, first soak with solvent, then clean with a brush, and LOCTITE 243 can be used again for locking after cleaning.

Q7: Does the storage condition of LOCTITE 243 have a great impact on the usage effect, and how to handle unused glue after opening?

A: Storage conditions have a huge impact on the usage effect of LOCTITE 243. If the storage temperature exceeds 28°C or is exposed to direct sunlight, it will cause premature curing, viscosity increase and even failure of the glue; unopened products should be stored in a dark place at 8–21°C with a 12-month shelf life. For unused glue after opening, seal it well and use it as soon as possible (recommended within 30 days), strictly prohibit pouring it back into the original bottle to avoid contaminating the entire bottle of glue.

Module 7: Technical Resources Download & Consultation

📥 Technical Document Download

•         LOCTITE® 243™ Technical Data Sheet (TDS) (PDF, Latest Version Nov 2020) 【Click to Download】

•         Safety Data Sheet (SDS/MSDS) (Multi-language version, including RoHS/REACH compliance statement) 【Click to Download】

•         LOCTITE 243 Threadlocking Process Guide (Including full process of application/curing/cleaning) 【Click to Download】

•         Threadlocking Substrate Compatibility Manual (Including activator selection guide) 【Click to Download】

🔧 Engineer Tools

•         Substrate/Activator Selection Assistant: Input thread substrate, clearance size, ambient temperature → generate customized application and curing scheme

•         Dispensing Amount Calculator: Automatically calculate the optimal single-piece dispensing amount according to thread specifications (M6-M16), reducing material waste

•         Working Condition Compatibility Query Tool: Input contact medium and service temperature, query product resistance performance and process optimization suggestions

📞 Consultation & Engineering Support

Assembly Application Engineering Laboratory provides you with:

•         Free process validation: Send your threaded workpieces, and we will issue a customized test report including locking torque, temperature aging resistance and medium tolerance

•         Remote/On-site glue testing: Bring dispensing tools and activators to your production line to verify the compatibility of LOCTITE 243 with existing equipment in real time

•         Cost optimization evaluation: Analyze your current threadlocking process and propose cost reduction and efficiency improvement schemes such as dispensing amount control and on-demand use of activators

•         Compliance consultation: Assist in completing the preparation of RoHS/REACH related compliance materials and provide product compliance certification documents

📋 Take Action Now

[Apply for Free Process Validation Report] | [Book On-site Glue Testing Service] | [Consult Application Engineer] | [Request Sample]

Make LOCTITE® 243™ your Medium Strength Removable Threadlocking Solution

Assembly – Your Industrial Adhesion Process Partner