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How To Select The Right Retaining Compound

Red bottle Loctite adhesives have been used in industrial applications for more than 50 years, but do you know the difference between the applications these can be used for and how to select the right one? This article looks at retaining compounds, or retainers, and how they fit in an MRO operative’s toolbox.

What is a Retaining Compound?

A retaining compound’s primary function is to securely bond bearings, bushes, and cylindrical parts into housings or on shafts. A type of anaerobic adhesive, that cures with the absence of air and the presence of an active metal, retaining compounds have a broad range of industrial applications, finding uses wherever joined components require high strength bonding and sealing solutions.

Loctite 638 being used on metal

Advantages of Retaining Compounds

Applied as a liquid, they fill surface irregularities and provide 100% contact between mating metal surfaces, eliminating the need for expensive replacement parts, time consuming machining, or the use of mechanical methods. In addition, retaining compounds offer high strength with simplified and less costly designs, and reduced dependence on machining tolerances. They eliminate corrosion and fretting, and improve the durability of assembly. They offer the ability to disassemble the component, and an even distribution of load and stress over the entire joint.

What is the difference between a Retaining Compound and a Threadlocker?

This question ultimately comes back to the application at hand and the substrate the adhesive is being used on.

Retaining compounds are typically higher strength and designed specifically for bonding cylindrical components that must resist usually torque and compressive loads. 

Threadlockers, however, are designed to prevent self-loosening, leakage, and corrosion of threaded fasteners. Choosing the correct type of adhesive is crucial within aerospace, automotive, rail, and heavy machinery applications, but when high strength bonding is required, retaining compounds are generally the right choice.

How do I select the right Retaining Compound for my application?

Three factors need to be considered when selecting a retaining compound for a particular application.

Gap Fill Requirements

Like other anaerobic adhesives in the Loctite portfolio, retaining compounds are designed to fill small gaps and surface irregularities. Loctite retaining compounds are available in a range of viscosities, with some specialist grades capable of filling gaps up to 0.5mm:

  • Gap Size – up to 0.15mm – typically lower viscosity products
  • Gap Size – between 0.15mm and 0.25mm – higher viscosity liquid products
  • Gap Size – between 0.25mm and 0.5mm – paste like products, possibly used with activator

Strength Requirements

Similarly to threadlockers, retaining compounds offer both high strength (for permanent bonds) and medium strength (for future disassembly). High strength retaining compounds offer a higher shear and compressive strength and can also be used in applications with high torsional loads.

Service Temperature Requirements

Most Loctite retaining compounds offer a service temperature range between -55°C and 150°C. However, certain products are able to withstand higher temperatures (between 180°C and 230°C) for applications subject to more extreme heat.

Featured Product: Loctite 603


Traditional methods for fastening cylindrical parts cause loosening and leakage. Loctite 603 can help.

With infinite microscopic imperfections that exist on even the most precisely machined surfaces, cylindrical parts are at high risk for loosening and leaking. Interference fits typically have only 20-40% effective contact area, which is limited to the peaks left behind by machining processes.

Micro-movement during dynamic loading can shear these away, allowing the joint to fail. Fixing these failures not only causes downtime, but is expensive.


  • Locks against shock and vibration
  • Increase shear strength, creating stronger assemblies
  • Seals against corrosion and leakage
  • Prevents ingress of moisture and other corrosion elements
  • Reduces inventory and maintenance costs


  • Colour - Green
  • Chemical Type - Methacrylate Ester
  • Viscosity - 125.0 MPA-S (CP)
  • Shear Strength Seal - 26.0 N/MM² ( 3770.0 PSI )
  • Temp Range - -55.0 °C - 150.0 °C ( -65.0 °F - 300.0 °F )
  • Fixture Time / Full Cure - 10.0 MIN.
Loctite 603 bottles