Loctite 243 thread lockers

LOCTITE 243 is a one-component anaerobic acrylic adhesive formulated with dimethacrylate ester chemistry and engineered for medium strength threadlocking applications. The uncured material appears blue in color and shows positive fluorescence under UV light for inspection control. It features medium viscosity with thixotropic characteristics, reducing liquid migration after application. The product cures when confined between close fitting metal surfaces in the absence of air and may be used with Activators 7471™, 7649™, 7088™, or 7091™ as a secondary cure system where faster curing is required. It is specifically developed for locking and sealing threaded fasteners in equipment such as pumps, gearboxes, motors, and vehicles.

The adhesive has a specific gravity of 1.08 at 25°C. Brookfield viscosity measured at 25°C using RVT with spindle 3 at 20 rpm ranges from 1,300 to 3,000 mPa·s (cP). Cone and Plate viscosity at 25°C with Cone 35/2 at 129 s⁻¹ is 350 mPa·s (cP). Cure performance depends on substrate type, bond gap, temperature, and activator usage. Breakaway strength development tested at 23°C on M10 steel nuts and bolts according to ISO 10964 shows effective curing on both active metals such as brass and passive materials including stainless steel and zinc dichromate. Shear strength development tested on steel pins and collars at controlled bond gaps according to ISO 10123 demonstrates that cure speed varies with thread quality, type, and size. Higher temperatures accelerate curing compared to 23°C baseline conditions.

After curing for 24 hours at 23°C, the product exhibits a glass transition temperature of 100°C according to ISO 11359-2. The coefficient of thermal expansion is 80 × 10⁻⁶ K⁻¹ below Tg and 90 × 10⁻⁶ K⁻¹ above Tg. Thermal conductivity measured as per ISO 8302 is 0.1 W/(m·K), and specific heat is 0.3 kJ/(kg·K). Breakaway torque performance according to ISO 10964 for unseated assemblies shows 22 N·m (200 lb·in) for M10 black oxide bolts with mild steel nuts, 9 N·m (80 lb·in) for M6 assemblies, 50 N·m (440 lb·in) for M16 assemblies, and 12 N·m (110 lb·in) for 3/8 x 16 steel nuts and bolts. Corresponding prevail torque values at 180° are 9 N·m (80 lb·in) for M10, 1 N·m (9 lb·in) for M6, 20 N·m (180 lb·in) for M16, and 8 N·m (70 lb·in) for 3/8 x 16 assemblies.

For assemblies pre-torqued to 5 N·m, breakloose torque values are 22 N·m (200 lb·in) for M10 black oxide bolts and 15 N·m (130 lb·in) for 3/8 x 16 steel nuts and bolts. Prevail torque at 180° under the same pre-torque condition measures 9 N·m (80 lb·in) for M10 and 6 N·m (50 lb·in) for 3/8 x 16 assemblies. Compressive shear strength tested according to ISO 10123 on steel pins and collars exceeds 7.6 N/mm² (1,100 psi). After one week at 23°C, breakloose torque on M10 zinc phosphate nuts and bolts reaches 30 N·m (270 lb·in), and on M10 stainless steel assemblies reaches 14 N·m (120 lb·in).

Environmental resistance testing after one week of curing at 23°C demonstrates strong durability across a wide temperature range. The product has been tested down to -75°C (-100°F), with potential functionality below this temperature although not formally tested. Chemical resistance testing shows excellent retention of initial strength after 500, 1000, and 5000 hours exposure. In motor oil at 125°C, strength retention ranges from 110% to 115%. In brake fluid at 23°C, retention increases up to 125% after extended exposure. Water/glycol 50/50 mixture at 87°C shows retention up to 130% after 5000 hours. Resistance in unleaded gasoline, ethanol, E85 ethanol fuel, and B100 bio-diesel remains high, while acetone exposure shows moderate strength retention. Exposure to 20% sodium hydroxide and 10% phosphoric acid at 23°C also maintains high performance levels over long durations.

This product is not recommended for use in pure oxygen or oxygen-rich systems and should not be used as a sealant for chlorine or strong oxidizing materials. It is generally not recommended for plastics, particularly thermoplastic materials where stress cracking may occur, and compatibility testing is advised before use on such substrates.

For assembly, surfaces should be cleaned with a LOCTITE cleaning solvent and allowed to dry. If faster curing is required, the appropriate activator should be applied and allowed to dry before adhesive application. The product must be shaken thoroughly before use, and care should be taken to avoid nozzle contact with metal surfaces to prevent clogging. For through holes, several drops should be applied to the bolt at the nut engagement area. For blind holes, the product should be applied to the lower third of the internal threads or to the bottom of the blind hole. For sealing applications, a 360° bead should be applied to the leading threads of the male fitting, leaving the first thread free and forcing the material into the threads to fill voids completely. Larger threads may require additional application to both male and female threads before assembly and tightening.

Disassembly is normally possible using standard hand tools. In cases of excessive engagement length, localized heating to approximately 250°C is recommended before disassembling while hot. Cured material may be removed by soaking in LOCTITE solvent followed by mechanical abrasion such as wire brushing.

The product should be stored in unopened containers in a dry location. Optimal storage temperature ranges from 8°C to 21°C. Storage below 8°C or above 28°C may adversely affect product properties. Contaminated material should not be returned to the original container. The technical data presented represent typical laboratory values under controlled conditions of 23±2°C and 50±5% relative humidity and are intended for reference guidance. Users are advised to conduct their own testing to confirm suitability for specific production processes and applications.