Loctite® 221 is a low-strength, low-viscosity purple threadlocker formulated for small metal fasteners. It provides secure locking while still allowing disassembly with standard hand tools. Designed to prevent loosening from vibration, it cures in confined spaces without air and remains reliable across a wide temperature range.
Loctite® 221 is ideal for locking and sealing small threaded fasteners up to M12 in diameter. It is particularly effective on set screws, calibration screws, or fasteners that may require occasional adjustment. Its low viscosity allows the adhesive to wick into threads, forming a durable bond between metal surfaces. Once cured, it resists vibration, prevents leaks, and helps reduce loosening during use. It performs well on a variety of metals, including stainless steel and brass, and cures fully within 24 hours. The removable nature of this product makes it suitable for delicate assemblies where disassembly is sometimes necessary.
Colour: Purple
Viscosity: 100 – 150 mPa·s
Fixture Time on Steel: ~25 minutes
Fixture Time on Brass: ~20 minutes
Fixture Time on Stainless Steel: ~210 minutes
Full Cure Time: 24 hours
Breakaway Torque: Approx. 8.5 Nm
Service Temperature Range: –55°C to +150°C
Specific Gravity: ~1.05
Recommended Substrates: Steel, stainless steel, brass
Packaging Sizes: Typically available in 10 ml, 50 ml, and 250 ml bottles
Primary Chemistry: Methacrylate ester
Low-strength formula designed for easy removal with hand tools
Low-viscosity liquid flows easily into fine threads and hard-to-reach areas
Provides a reliable seal against vibration, shock, and minor contamination
Suitable for use on less active metals such as stainless steel
Performs in a broad temperature range from –55°C to +150°C
Prevents small threaded fasteners from loosening due to vibration or thermal expansion
Reduces the risk of leaks or corrosion in threaded assemblies
Enables secure fastening without the need for mechanical locking methods
Simplifies maintenance by allowing for tool-free disassembly of bonded parts
Designed for use on small threaded fasteners up to M12
Effective on set screws, collars, bolts, and similar hardware where occasional removal is required
Performs well on both active and passive metals
Commonly used in electrical equipment, industrial maintenance, and light mechanical assemblies
Can be applied without disassembly in some cases due to low-viscosity wicking ability
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