Loctite GRADE C

Overview

Loctite Grade C (Letter Grade C / 084) is a blue, low-viscosity, medium-strength anaerobic threadlocker designed to lock and seal fine threaded fasteners. It flows easily into tight clearances, cures in the absence of air between metal surfaces, and forms a tough plastic that bonds the threads together.

Once cured, Loctite Grade C:

• Helps prevent loosening from shock, vibration and cyclic loading

• Seals the thread helix against micro-leaks of fluids and gases

• Provides ongoing protection against corrosion and fretting on engaged threads

It is widely used in legacy and specification-driven applications where a letter-grade product is required rather than a modern numeric Loctite code.

Why choose Loctite Grade C?

1) Medium strength – secure but serviceable
Grade C is a medium-strength threadlocker: it keeps fasteners locked under vibration yet can still be removed with ordinary hand tools. This makes it ideal for equipment that must be secure in service but can’t be “permanently” locked like with a high-strength red grade.

2) Low-viscosity wicking behavior
With a viscosity typically in the 10–25 cP range, Loctite Grade C flows easily into fine threads and close-tolerance fits, either before assembly or by wicking into pre-assembled joints via capillary action.

3) Optimized for fine threaded nuts, bolts and studs
The product is specifically recommended for fine-pitch fasteners, where standard or high-viscosity threadlockers may not fully penetrate the engagement.

4) Military-grade heritage
Loctite Grade C is one of the original blue, letter-grade threadlockers, designed to meet MIL-S-22473E Grade C / ASTM D5363 requirements. It’s commonly used to support existing drawings and aerospace/defense-style specifications that still call out this grade.

5) Easy quality control
Grade C is fluorescent blue under UV light

Typical Applications

• Locking and sealing fine threaded nuts, bolts and studs in:

  • Precision machinery and instrumentation

  • Aerospace, defense and legacy equipment designed around MIL letter grades

  • Hydraulic and pneumatic connections using fine-thread fasteners

• Assemblies where medium-strength retention and serviceability with tools are both required

• Pre-assembled joints where threadlocker must wick into existing threads rather than be applied before assembly

Loctite Grade C is formulated for metal-to-metal threads and is not recommended for plastics or for pure oxygen / strong oxidizer environments.

How to Use Loctite Grade C

Method A – Before assembly

1. Surface preparation

   • Mechanically clean threads to remove loose rust, dirt and old threadlocker.

   • Wipe away heavy oils, grease and anti-seize.

   • Light oil films are often tolerated, but cleaner metal gives more consistent results.

2. Apply

   • Shake the bottle.

   • Apply a continuous bead of Loctite Grade C along the male threads, or a small ring inside the female threads, covering the intended engagement length.

3. Assemble and torque

   • Assemble parts promptly and tighten to the specified torque.

   • Avoid repeated loosening and re-tightening once curing has begun.

4. Cure

   • Allow the joint to remain undisturbed until handling strength is reached.

   • For full performance, allow approximately 24 hours at room temperature before subjecting the joint to maximum load or vibration.

Method B – Wicking into pre-assembled joints

1. Assemble the fastener and torque it to its final position.

2. Apply Loctite Grade C at the thread exit or nut/bolt interface, letting it sit so the low-viscosity liquid can wick into the threads by capillary action.

3. Allow sufficient time for penetration and curing before loading the joint fully.

Disassembly

• Loctite Grade C is medium-strength and is typically removable with normal hand tools (wrenches, sockets).

• For large or long-service fasteners, extra leverage or an impact tool may be helpful. Heat is usually not required, but can be used carefully if threads are stubborn.

Safety & Handling

Based on typical SDS information for Loctite letter-grade threadlockers:

• May cause skin and eye irritation upon contact.

• Prolonged or repeated exposure may lead to skin sensitization in susceptible individuals.

• Vapors or mists can cause mild respiratory irritation in poorly ventilated areas.

• Uncured product may be harmful to aquatic life if released uncontrolled.

Recommended precautions

• Use in a well-ventilated area.

• Avoid contact with skin and eyes; wear safety glasses and suitable protective gloves.

• Wash hands thoroughly after handling and before eating or drinking.

• Do not discharge uncured product into drains or natural waterways.

• Store in the original, tightly sealed container in a cool, dry place away from heat and direct sunlight.

Always consult the latest Safety Data Sheet (SDS) for Loctite Grade C valid in your region before use.

FAQs

Q1: What is Loctite Grade C used for?
Loctite Grade C is a blue, low-viscosity, medium-strength threadlocker used to lock and seal fine threaded nuts, bolts and studs, especially in specification-driven or legacy applications where a letter-grade product is required.

Q2: How is Grade C different from Grade A or numeric threadlockers like 242/243?

• Grade C: Blue, medium strength, low-viscosity wicking grade for fine threads, removable with tools.

• Grade A: Red, high-strength wicking grade where removal usually requires heat.

• 242/243: Modern blue medium-strength threadlockers with higher viscosity for general-purpose pre-assembly use rather than fine-thread wicking.

Q3: Is Loctite Grade C removable?
Yes. Grade C is medium strength, designed so that fasteners can be removed later with standard hand tools, while still providing strong resistance to vibration loosening in service.

Q4: Can Loctite Grade C be used on stainless steel or plated fasteners?
Yes. It can be used on common metals, including stainless and plated hardware. However, cure may be slower on passive metals, so allow additional curing time before applying full load or vibration.

Q5: Is Grade C oil-tolerant?
Loctite Grade C can usually cure through light films of oil, but heavy oil, grease or anti-seize should be removed for best performance, particularly in critical or high-stress applications.

Q6: Can I use Loctite Grade C on plastic threads?
No. Like other anaerobic threadlockers, Grade C is intended for metal-to-metal threads and can cause stress cracking in certain plastics. It also will not properly cure on non-metallic surfaces.

Q7: Does Loctite Grade C also act as a sealant?
Yes. By filling the gap between male and female threads, Grade C locks and seals in a single step, helping prevent fluid and gas leakage along the thread helix and reducing corrosion. It is not a replacement for flange gaskets on mating faces, but it is very effective for sealing through-thread leak paths.