LOCTITE® 661 is a high strength retaining compound designed for bonding cylindrical metal parts that require reliable, gap-filling performance. It provides fast fixture times, high temperature resistance, and exceptional holding power for industrial assemblies exposed to vibration or heavy loads.
Colour: Amber
Viscosity: 400 to 600 mPa·s at 25 °C
Fixture time: 4 to 10 minutes on steel
Shear strength (steel): 15 to 25 N/mm² after full cure
Temperature resistance: –55 °C to +175 °C
Maximum diametral clearance: 0.15 mm
Cure method: Anaerobic (cures in absence of air between metal surfaces)
Primary Chemistry:
Methacrylate ester
Conor Robertson, Technical Specialist
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Fast answers to formulation and application questions.
LOCTITE® 661 is formulated to retain bearings, bushings, shafts, and cylindrical fittings under high stress and demanding conditions. Its anaerobic chemistry cures in the absence of air when confined between close-fitting metal surfaces, forming a strong, thermoset polymer that locks assemblies in place and prevents loosening due to vibration or thermal cycling. This compound offers high shear strength and a service temperature range up to +175 °C, making it ideal for use in power transmission systems, electric motors, pumps, and industrial machinery. It also provides excellent gap-filling capability, allowing it to bond worn or slightly out-of-tolerance parts with secure, long-lasting performance.
Eliminates loosening and slipping between metal components caused by mechanical stress.
Replaces the need for mechanical locking devices such as keys, pins, or splines.
Reduces downtime and maintenance costs by preventing premature part failure.
Restores strength to worn or out-of-tolerance assemblies, extending component life.
Prevents corrosion and fretting wear in close-fitting cylindrical assemblies.
LOCTITE® 661 should be applied to clean, dry metal surfaces before assembly. Once the parts are fitted together, the adhesive cures anaerobically to form a strong, high-strength bond. It is ideal for retaining bearings, bushings, gears, and sleeves on shafts or in housings. For large gaps or inactive metals, an activator such as LOCTITE® SF 7649 can be used to speed up the curing process. Once cured, assemblies can be disassembled using localised heat and standard hand tools if necessary.
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