Loctite 573: The Best Anaerobic Flange Sealant for Metal Assemblies
Recent studies show that nearly 60% of unscheduled machinery downtime in manufacturing and automotive sectors originates from flange sealing failures or gasket deterioration. For engineers and maintenance professionals, these issues can lead to costly leaks, reduced efficiency, and unplanned shutdowns. That’s where Loctite 573 proves invaluable — a green, medium-strength anaerobic flange sealant formulated to provide a reliable, long-lasting seal on rigid metal surfaces.
Designed for machined flanges, gearboxes, pumps, and engine casings, Loctite 573 eliminates the need for conventional paper or rubber gaskets by forming a tough, chemical-resistant seal directly between metal faces.
In this comprehensive review, we’ll explore how Loctite 573 works, its technical specifications, application procedure, curing behavior, and performance benefits. We’ll also discuss its closest equivalents, recommended uses, and share a demonstration video illustrating real-world application and results — showing why it remains a trusted choice for industrial maintenance and precision assembly.
What is Loctite 573?
Loctite 573 is a medium-strength anaerobic flange sealant designed for rigid metal faces and flanges. It forms an in-place gasket when confined between close-fitting metal surfaces, curing in the absence of air to create a durable, leak-proof seal.
It’s part of Henkel’s Loctite gasketing range and is particularly suited for large, rigid metal flanges—like gearbox and engine casings—where assembly might take several hours.
Unlike traditional paper or cork gaskets that can deform or shrink over time, Loctite 573 fills microscopic surface irregularities to prevent leaks of gases and liquids, even under pressure or vibration.
Key Benefits of Loctite 573
✅ Ideal for rigid metal flanges: Works perfectly on cast iron, steel, and aluminum surfaces.
✅ Slow curing formula: Allows long assembly times without premature curing — ideal for complex assemblies.
✅ Excellent fluid resistance: Stands up to motor oils, glycol, water, and even gasoline.
✅ Medium viscosity, thixotropic formula: Prevents running or dripping after application.
✅ UV fluorescence: Makes it easy to inspect the seal under UV light.
✅ Reliable sealing: Reduces chances of micro-leakage and gasket blowout.
Where Loctite 573 is Used
This product is a favorite in industries where rigid flange sealing is critical. Common applications include:
| Industry | Application Areas |
|---|---|
| Automotive | Gearboxes, engine casings, oil pans, differential housings |
| Manufacturing | Pump housings, compressor flanges, metal casings |
| Marine | Engine blocks, gear assemblies, fluid transfer systems |
| Heavy Machinery | Hydraulic systems, steel flanges, and cast housings |
Essentially, if you’re sealing close-fitting, rigid metal flanges, Loctite 573 is made for you.
How Loctite 573 Works
Loctite 573 is based on dimethacrylate ester chemistry. It remains liquid in the presence of air but begins to cure once confined between metal surfaces (where oxygen is absent). The absence of air triggers polymerization, forming a solid seal that resists vibration, heat, and fluids.
It’s part of the anaerobic adhesive family, which includes other Loctite flange sealants like Loctite 574 and Loctite 518.
Loctite 573 Technical Specifications
| Property | Value / Description |
|---|---|
| Chemical Type | Dimethacrylate ester |
| Color (Uncured) | Green paste |
| Cure Type | Anaerobic (no air) |
| Strength | Medium |
| Viscosity (at 25°C) | 13,500 – 33,000 mPa·s |
| Temperature Range | -55°C to +150°C |
| Compressive Shear Strength | ≥1.5 N/mm² |
| Lap Shear Strength (Steel) | 1.3 N/mm² |
| Tensile Strength | 5 N/mm² |
| Cure Speed (22°C) | Handling time: ~1 hour; Full cure: 24 hours |
| Fluorescence | Positive under UV light |
| Packaging Sizes | 50ml, 250ml tubes |
What is Loctite 573 Used For?
Loctite 573 is primarily used to seal close-fitting joints between rigid metal surfaces, such as:
- Gearboxes
- Engine casings
- Oil pans
- Hydraulic components
- Compressor and pump housings
It’s perfect for flanges that don’t flex under load — because flexibility would break the cured seal.
If you’ve got metal-to-metal joints and need a reliable, fluid-tight seal, Loctite 573 should be your go-to.
Loctite 573 vs Loctite 574: What’s the Difference?
Both are flange sealants from Loctite, but they differ in curing speed and application:
| Feature | Loctite 573 | Loctite 574 |
|---|---|---|
| Cure Speed | Slow (for long assembly times) | Fast (for production environments) |
| Viscosity | Medium | Medium-high |
| Color | Green | Orange |
| Ideal for | Large assemblies with slow fit-up | Fast repairs or smaller flanges |
| Gap Fill | Up to 0.25 mm | Up to 0.25 mm |
If you’re assembling slowly (like during maintenance or inspection jobs), Loctite 573 gives you more working time. If speed matters (like in automated assembly lines), Loctite 574 is a better fit.
Loctite 573 Equivalent Products
If Loctite 573 isn’t available in your region, here are some equivalents that perform similarly:
| Brand | Equivalent Product |
|---|---|
| Permatex | Anaerobic Gasket Maker 51813 |
| ThreeBond | 1104B Liquid Gasket |
| Dirko | Dirko HT Sealant |
| Weicon | Flange Sealant AN 302-70 |
| Loctite Alternative | Loctite 574 (faster cure version) |
Always check the chemical compatibility and curing characteristics before substitution.
How to Use Loctite 573 – Step-by-Step Application Guide
Here’s how to apply Loctite 573 correctly for a perfect seal:
Step 1: Surface Preparation
Clean the metal surfaces thoroughly. Remove grease, oil, and dirt using Loctite SF 7063 or Loctite SF 7070 cleaner.
🧴 Pro tip: Clean surfaces mean stronger bonds.
Step 2: Check the Gap
Loctite 573 is ideal for close-fitting flanges with a gap up to 0.25 mm. For larger gaps, apply on both flange faces.
Step 3: Apply the Sealant
- Apply a continuous bead or rolled film to one flange face.
- For flanges with large diameters, a pen roller gives even coverage.
- Avoid excessive product — a thin, even layer is perfect.
Step 4: Assemble the Parts
Join the flanges together immediately after application.
Tighten bolts as soon as possible to prevent shimming or air pockets.
Step 5: Curing
Allow the assembly to sit at room temperature.
- Handling strength: 1–2 hours
- Full cure: 24 hours at 22°C
- Cure time can be accelerated using Loctite Activator SF 7471 or SF 7649.
Step 6: Testing the Seal
Once cured, pressure-test the joint (<0.5 MPa) to verify the seal.
Cure Time for Loctite 573
Loctite 573 cures anaerobically, meaning it hardens when oxygen is absent and metal ions are present.
- At 22°C: Full cure in 24 hours
- At 40°C: Cure time reduces significantly
- With Activator SF 7649: Full cure within 6 hours
- On inactive metals (e.g., stainless steel): Use activator to improve cure speed
Storage and Handling
Store between 8°C and 21°C.
Avoid freezing or storing above 28°C.
Keep container tightly sealed.
Never return unused product to the original bottle (to prevent contamination).
Loctite 573 Safety and SDS Information
Like most industrial sealants, Loctite 573 requires careful handling:
- Avoid direct contact with skin and eyes.
- Use in a well-ventilated area.
- Refer to the Loctite 573 SDS for detailed safety instructions.
Download official Safety Data Sheet (SDS) and Technical Data Sheet (TDS) from Henkel’s official site.
Where to Buy Loctite 573
You can buy Loctite 573 from authorized distributors or trusted eCommerce platforms:
Always ensure the product is genuine Henkel Loctite, as counterfeit adhesives are common in the market.
Pro Tips for Professionals
Always use Loctite cleaners before sealing.
For faster curing, apply Loctite Activator 7649.
Avoid using on flexible plastic or rubber surfaces.
Once opened, use within the recommended shelf life for best performance.
Inspect using UV light to confirm complete coverage.
Conclusion: Why Loctite 573 is Still a Top Choice
In the world of industrial maintenance and assembly, Loctite 573 continues to hold its reputation as a reliable flange sealant for rigid metal assemblies.
Its slow curing speed gives technicians the freedom to take their time with alignment and tightening, while its excellent chemical resistance ensures long-term reliability.
Whether you’re sealing gearboxes, pumps, or engine flanges, Loctite 573 guarantees a leak-free, vibration-resistant seal that stands the test of time.
If you value precision, performance, and peace of mind in every joint you seal — Loctite 573 is worth every drop.