A loose bearing costs far more than the bearing itself. When a bearing spins on a shaft or rocks in its housing — what engineers call "spinning" or "fretting" — you're looking at shaft damage, housing bore damage, heat generation, premature bearing failure, and unplanned downtime. Loctite retaining compound is the maintenance engineer's tool for addressing inadequate fits, salvaging worn bores, and locking correct-clearance cylindrical assemblies permanently.
This guide covers every Loctite retaining compound grade AIMS stocks — 609, 620, 635, 638, 641, 648, 660 and 680 — with real selection criteria, installation steps, and troubleshooting for bearing and cylindrical-fit applications across Australian industry.
What Is a Loctite Retaining Compound?
Loctite retaining compounds are anaerobic adhesives designed specifically for cylindrical assemblies — shafts and bores, bearings and housings, pulleys and hubs, bushes and bores. They cure when confined between close-fitting metal surfaces in the absence of air, filling the microscopic voids in the interface and creating a bond that resists both axial and rotational loads.
They are not thread sealants, and they are not threadlockers — though all three are anaerobic Loctite products. Retaining compounds are formulated for larger-gap, higher-viscosity, cylindrical-joint applications where threadlockers would either cure too fast or lack the gap-filling properties needed.
Retaining Compound vs Press Fit: When to Use Each
Press fit (interference fit) relies on the elastic deformation of mating parts to create holding force. Retaining compound supplements or replaces that mechanical interference.
Use retaining compound when:
- The engineering specification calls for it (adhesive joint design)
- The bore has worn to a clearance (transition) fit and re-machining isn't economic
- The application requires easy assembly of parts that need precise location before locking
- The press force required for full interference fit would damage the bearing or shaft
- You are salvaging a worn bore up to 0.50 mm oversized (using Loctite 660)
Press fit alone is still the right choice when:
- The specification calls for a standard H7/p6 or similar interference fit
- The assembly will regularly be disassembled and rebuilt (retaining compound is more difficult to remove cleanly than a press fit to re-establish)
- The bearing housing material doesn't give adequate surface for adhesive cure
Both together: Press-fit plus retaining compound is used in high-load or high-shock applications where the press fit provides immediate holding force and the retaining compound provides long-term retention and fretting corrosion prevention.
The Key Selection Variable: Diametral Clearance
Every Loctite retaining compound has a maximum diametral clearance it can bridge effectively. This is the single most important specification for grade selection.
Diametral clearance is the difference in diameter between the shaft (or bearing OD) and the bore it fits into. On a 50 mm shaft fitting a 50.10 mm bore, the diametral clearance is 0.10 mm.
Exceed the product's maximum clearance and it either won't fill the gap, won't cure consistently through the full joint, or won't develop adequate bond strength.
Loctite Retaining Compound Comparison Chart
⚠️ Verify before specifying: Specifications below are drawn from Loctite published data and AIMS's own product data sheets. Always cross-check against the current Technical Data Sheet (TDS) for the specific grade before specifying for engineering applications.
| Grade | Max Diametral Clearance | Shear Strength | Service Temp | Fixture Time (22°C) | Disassembly | Best Use |
|---|---|---|---|---|---|---|
| 609 | 0.15 mm | 2,300 psi (15.9 MPa) | –54°C to 150°C | 10 min | Difficult — heat required | Press-fit augmentation, low-clearance precision parts |
| 641 | 0.15 mm | 1,700 psi (11.7 MPa) | –54°C to 150°C | 20 min | Moderate — heat recommended | Standard bearing installation, planned disassembly |
| 638 | 0.25 mm | 4,500 psi (31.0 MPa) | –54°C to 180°C | 4 min | Very difficult — heat required | High-strength slip-fit, large bearing ODs |
| 648 | 0.15 mm | 3,900 psi (26.9 MPa) | –54°C to 180°C | 3 min | Very difficult — heat required | High-strength, rapid fixture, oil-tolerant, food-grade certified |
| 620 | 0.15–0.25 mm | ~3,770 psi (26.0 MPa) | –55°C to 230°C | See TDS | Very difficult — heat required | High-temperature cylindrical bonding above 180°C |
| 635 | Up to 0.15 mm | Very high (see TDS) | See TDS | 6 min | Very difficult — heat required | Maximum strength, no-fretting, production assembly |
| 660 | 0.50 mm | 3,335 psi (23.0 MPa) | –54°C to 150°C | 20 min | Difficult — heat required | Worn bore salvage and repair |
| 680 | 0.38 mm | 4,000 psi (27.6 MPa) | –54°C to 180°C | 4 min | Very difficult — heat required | General slip-fit, oil-tolerant, medium-large clearance |
Grade-by-Grade Breakdown
Loctite 609 — Press-Fit Augmentation
609 is a low-viscosity product designed to wick into the interface of already-pressed assemblies. If you have a part that's press-fitted but you want the additional retention and fretting prevention of retaining compound, 609 is applied after pressing — it flows into the interface by capillary action.
It's not the right choice for a slip-fit assembly. The viscosity is too low to remain in the bore gap during assembly, and the bond strength is the lowest in the retaining compound range.
Primary applications: Augmenting press-fit gears, pulleys, and bushes; capillary application after assembly where 641 or 638 would have been preferred but wasn't applied.
Loctite 641 — The Standard Bearing Retainer
641 is the industry default for bearing installation. It has the lowest shear strength in the range, which sounds like a disadvantage but is often an advantage in practice: it allows planned disassembly for bearing replacement without thermal treatment or excessive risk of housing/shaft damage.
The 20-minute fixture time gives adequate assembly time for most bearing fits — you have enough working time to press or slide the bearing into position and align it before the product begins to cure.
Primary applications:
- Standard anti-friction bearing installation (deep groove ball, cylindrical roller, tapered roller, spherical roller)
- Sleeve bearings and plain bushes in standard fits
- Pulley and sprocket installation where removal for maintenance is planned
- Any cylindrical assembly requiring a permanent lock with manageable disassembly
Clearance note: 641 handles up to 0.15 mm diametral clearance. For shaft-bearing OD fits in the J7/h6 to H7/k6 range, you'll typically be within this limit. For larger clearances from wear, step up to 680 or 660.
Loctite 638 — High-Strength Slip-Fit
638 is one of the highest-shear-strength products in the range and handles a large clearance for a non-repair compound. It's oil-tolerant, meaning it cures reliably on surfaces with light oil contamination — important in environments where perfect cleaning isn't always achievable.
The 4-minute fixture time means you must work fast. Have both parts prepared, the product applied, and be ready to assemble before you start applying the product. With 638, you don't have time to pause.
Primary applications:
- High-load bearing installation where maximum retention is required
- Bearings with larger clearance fits (worn housing bores within 0.25 mm)
- Industrial gearboxes and high-torque assemblies
- Applications where service temperature reaches 150°C+
When to choose 638 vs 641: Choose 638 when bond strength is the priority and you don't anticipate regular disassembly. Choose 641 when manageable disassembly is important.
Loctite 648 — Rapid Fixture, High Strength
648 is the rapid-cure high-strength option. It combines nearly the strength of 638 with a 3-minute fixture time, and it's oil-tolerant. NSF/ANSI 61 and CFIA certified, which matters for food and beverage applications.
The 3-minute fixture time is both an advantage and a constraint. In production environments where throughput matters, 648 allows rapid assembly and immediate loading. In single-unit maintenance work, 3 minutes is very tight — practice the assembly sequence before applying product.
Primary applications:
- Production-rate bearing installation
- Food and beverage processing equipment (certified grade)
- High-strength retention at 0.15 mm or less clearance
- Applications at 150°C+ where 641 isn't rated
Loctite 620 — High-Temperature Retaining Compound
620 is the grade for cylindrical joints that run hotter than the standard range can handle. On AIMS's own product data, 620 carries a shear strength of 26.0 N/mm² (approximately 3,770 psi), a 0.15–0.25 mm gap-fill range, and a service range of –55°C to 230°C — well above the 150–180°C ceiling of 609, 641, 638, 648, 660 and 680.
Use 620 for:
- Locating pins in radiator and heat-exchanger assemblies
- Sleeves in pump housings running above 180°C
- Bearings in automotive transmissions and other elevated-temperature drivetrain components
- Any cylindrical fit where 638, 648 or 680's 180°C ceiling isn't sufficient
What 620 won't do: It isn't the right choice for standard-temperature bearing work — 641 or 638 are more widely stocked and easier to work with for anything running below 180°C. Confirm exact fixture time against the current TDS before specifying for a fast-cycle production line.
Loctite 635 — Maximum-Strength Retaining Compound
635 is positioned by Loctite as the strongest cylindrical bond in the range. On AIMS's own product data it fills the full gap between mating surfaces (up to 0.15 mm diametral clearance, viscosity 1,500–2,500 mPa·s) and fixtures in 6 minutes — fast enough for production assembly without the very tight window of 638 or 648.
Use 635 for:
- Maximum load transmission where 638 or 648's strength isn't quite enough
- Production assembly where a 6-minute fixture window is manageable but a 3–4 minute window (648/638) is too tight
- Applications where fretting and micro-movement at the interface must be eliminated entirely
What 635 won't do: A specific published shear strength figure and service temperature range weren't available on AIMS's product data — confirm both against the current Loctite TDS before specifying 635 for a safety-critical or high-temperature application.
Loctite 660 — Worn Bore Salvage
660 is in a class of its own. A 0.50 mm diametral clearance capability means it can salvage bearing housings that would otherwise require either re-machining and sleeving (expensive) or complete replacement of the housing component.
The product has a paste-like thixotropic consistency — it stays in the bore during assembly rather than running out. The 20-minute fixture time gives adequate assembly time despite the large gap.
Important: 660 is a repair product, not a standard installation product. It should not be used as a substitute for correct-clearance fits in normal maintenance. If a bore is that worn, investigate the root cause — if the bearing was fretting, the solution is retaining compound plus addressing the vibration or loading cause, not just a larger-gap compound.
Primary applications:
- Worn housing bore repair (0.25–0.50 mm clearance)
- Emergency field repair where re-machining isn't possible
- Salvaging pump and gearbox housings
Loctite 680 — Oil-Tolerant General Purpose
680 fills the gap between 638 (0.25 mm limit) and 660 (repair grade). It handles clearances up to 0.38 mm, is oil-tolerant, and has very high shear strength. For workshops dealing with aged equipment where bores have worn moderately, 680 is often the right general-purpose compound.
NSF/ANSI 61 and ABS certified. The 4-minute fixture time means a similar discipline to 638 — be ready before you start.
Primary applications:
- Standard slip-fit installation with moderate clearance
- Equipment with naturally larger fits (older designs, metric-imperial conversions)
- Environments where perfect surface cleanliness isn't achievable
Selecting the Right Grade: Decision Framework
Step 1: Measure the diametral clearance
Use a bore gauge and micrometer to determine actual shaft OD and bore ID. Calculate: Clearance = Bore ID − Shaft OD.
| Clearance | Grades available |
|---|---|
| Up to 0.15 mm | 609, 620, 635, 641, 648 |
| 0.16–0.25 mm | 620, 638 |
| 0.26–0.38 mm | 680 |
| 0.39–0.50 mm | 660 (repair) |
Step 2: Is disassembly planned?
- Yes, within service life → 641 (easiest disassembly)
- No, or only with significant effort acceptable → 638, 648, 620, 635 or 680
Step 3: Service temperature?
- Under 150°C → Any grade
- 150–180°C → 638, 648, or 680
- 180–230°C → 620
- Above 230°C → No standard retaining compound is rated for this; engineering review required
Step 4: Surface condition?
- Clean, dry steel → Any grade
- Minor oil contamination → 638, 648, or 680 (oil-tolerant)
- Passive metals (stainless, aluminium) → Apply Loctite 7649 Activator N first
Step 5: Is this a worn bore repair?
- Yes, clearance 0.26–0.50 mm → 660 or 680
- Yes, but root cause investigation still needed → proceed with repair AND address the cause
Step 6: Is maximum bond strength the priority, above all else?
- Yes, and a 6-minute assembly window is workable → 635
- Yes, and a faster 3–4 minute window is workable → 638 or 648
Step-by-Step Bearing Installation with Retaining Compound
This procedure covers standard bearing installation using Loctite 641 (or substitute your selected grade).
What you need:
- Loctite 641 (or selected grade)
- Loctite 7063 Cleaner/Degreaser
- Loctite 7649 Primer N (for stainless or aluminium housings/shafts)
- Clean lint-free cloths
- Bearing fitting tool or press
- Dial indicator (if checking alignment)
- Gloves
Procedure:
- Measure and confirm clearance. Before cleaning anything, measure the actual fit. Confirm the diametral clearance is within your selected grade's limit. If it's not, select a different grade or address the bore condition.
- Degrease all surfaces. Clean the shaft journal, bearing bore, housing bore, and bearing OD thoroughly with Loctite 7063. Wipe with clean cloths and allow to fully evaporate. The surface must be dry — solvent remaining on the surface inhibits cure.
- Apply activator if required. For stainless shafts or aluminium housings, apply Loctite 7649 Primer N to all mating surfaces. Allow 5–10 minutes to flash off completely.
- Apply retaining compound. Apply a thin bead of retaining compound around the bearing OD and/or the housing bore. For 641 and 660, you have adequate working time. For 638, 648, 620 and 635, apply and assemble promptly — these grades don't give you long to pause.
- Assemble the bearing. Install using a proper bearing fitting tool or press. Apply force through the bearing ring that is being seated (inner ring on shaft, outer ring in housing) — never drive a bearing by hammering on the opposite ring through the rolling elements. Seat fully and check alignment.
- Remove excess compound. Wipe any squeeze-out from accessible areas with a clean cloth and solvent before it cures. Cured squeeze-out can be difficult to remove cleanly.
- Allow cure before loading. With 641, handling strength is reached in 20 minutes. Full load should wait 24 hours. With 638, 648 or 635, handling strength is reached in 3–6 minutes, but full cure still requires 24 hours.
- Verify. After cure, check that the bearing has not migrated and is seated squarely. On critical installations, verify with a dial indicator.
Disassembly and Removal
Loctite 641: Heat the housing to 80–100°C. Most 641-bonded bearings release at this temperature with normal extraction force. A bearing puller at temperature will remove most assemblies cleanly.
Loctite 638, 648, 680, 620, 635: Heat required to 200°C or above (for 620, allow for the fact that its 230°C service rating means the cured bond itself tolerates more heat before it starts to release — expect to work at the top of this range or above). Allow heat to soak through the housing mass — surface temperature alone is not sufficient. Apply extraction force while hot. Be prepared that even at temperature, high-strength grades may require significant force.
Loctite 660 (worn bore repair): Disassembly of 660-bonded assemblies is difficult by design. This is a repair product — the goal is permanence. Heat to 200°C+ and expect to work hard.
General disassembly notes:
- Never attempt cold removal on retaining compound bonded assemblies — you will damage the shaft, housing, or bearing
- On aluminium housings, limit heat to 150°C maximum to avoid distortion
- For large or complex assemblies, oven heating is more consistent than spot heating
Common Failures and How to Avoid Them
Failure: Bearing spins after installation despite retaining compound
- Cause 1: Clearance exceeded the product's limit — measure the bore before specifying
- Cause 2: Incomplete degreasing — any oil contamination on non-oil-tolerant grades prevents cure
- Cause 3: Passive metal (stainless shaft) without activator — no cure will occur
- Cause 4: Temperature too low — below 10°C cure is very slow; extend cure time or warm the assembly
Failure: Bond doesn't hold in service
- Cause 1: Insufficient cure time before full loading
- Cause 2: Service temperature exceeds the product's rating — check whether 620 (rated to 230°C) is needed instead of a standard grade
- Cause 3: Radial load or shock exceeds the bond's capability — retaining compound has limits; check engineering calculations for the application
Failure: Can't remove the bearing
- Cause 1: Used 638, 648, 620 or 635 where 641 should have been selected (and disassembly was planned)
- Cause 2: Insufficient heat during extraction — surface temperature isn't the same as through temperature on a large housing mass
- Solution: Apply heat, wait longer, ensure the entire housing mass is hot, then use a proper extraction tool
Failure: Compound cures before assembly is complete
- Cause 1: Using 638, 648 or 635 (3–6 minute fixture time) without preparation
- Cause 2: High ambient temperature accelerating cure
- Solution: Plan the assembly sequence completely before applying product. For fast-fixture grades, have a second person assist — one applies product, one assembles.
Frequently Asked Questions
What Loctite do I use to mount a bearing?
Loctite 641 is the standard default for bearing installation. It handles diametral clearances up to 0.15 mm, has a manageable 20-minute fixture time, and can be disassembled with heat if needed. For larger clearances, move to 680 (up to 0.38 mm) or 660 (up to 0.50 mm for worn bore repair). For permanently bonded high-load applications, use 638 or 635; for service above 180°C, use 620.
What is the difference between Loctite 641 and 638?
641 is medium strength (1,700 psi shear) with a 20-minute fixture time, designed for assemblies where future disassembly is anticipated. 638 is high strength (4,500 psi shear) with a 4-minute fixture time, oil-tolerant, and rated to 180°C — designed for permanent, high-load retention. Choose 641 when you'll need to change bearings; choose 638 when you want maximum retention.
Can you use Loctite on bearings?
Yes — this is one of the most common uses for Loctite retaining compound. It bonds the bearing's inner ring to the shaft and/or the outer ring to the housing bore, filling the microscopic clearance between the parts to stop the bearing spinning or fretting in service. 641 is the standard grade for this; 638, 648, 620 and 635 are used where higher strength, faster fixture, or higher temperature service is needed.
What are the differences between Loctite 620 and 680 retaining compounds?
The deciding factor is temperature. 680 is rated to 180°C and handles a larger clearance (up to 0.38 mm); 620 is rated to 230°C but fills a narrower gap (0.15–0.25 mm). If the application runs below 180°C, 680's broader clearance range and established track record make it the simpler choice. Above 180°C, 620 is the only grade in the AIMS range rated for the job.
What is the strongest Loctite retaining compound?
Loctite 635 is positioned as the maximum-strength grade in the cylindrical retaining compound range, ahead of 638 and 648 on bond strength, though a specific published shear figure wasn't available on AIMS's own product data — confirm against the current TDS if you need an exact number for an engineering calculation. Among grades with a confirmed shear figure, 638 (4,500 psi) is the highest.
What is Loctite 680 retaining compound used for?
680 is a general-purpose, oil-tolerant retaining compound for slip-fit cylindrical assemblies with moderate clearance — up to 0.38 mm diametral. It sits between 638 (0.25 mm limit, faster fixture) and 660 (repair grade, up to 0.50 mm). Typical uses are bearing and bush installation on aged equipment where bores have worn moderately, and any application where perfect surface cleanliness isn't achievable.
Can I use Loctite retaining compound on aluminium?
Yes, but aluminium is a passive metal that inhibits anaerobic cure. Apply Loctite 7649 Activator N to both surfaces (shaft and bore) and allow 5–10 minutes to flash off before applying compound. Without activator, expect poor or no cure on aluminium.
How much clearance can Loctite retaining compound fill?
Depends on the grade: 641, 620 and 635 handle up to 0.15 mm diametral clearance (620 extending to 0.25 mm), 638 up to 0.25 mm, 680 up to 0.38 mm, and 660 up to 0.50 mm for worn bore repair. Exceeding these limits results in inconsistent bond strength and potential failure.
How do you remove a bearing that's been locked with Loctite?
Heat the assembly to 150–200°C (depending on grade used) and apply extraction force while hot. For 641, 150°C is usually sufficient. For 638, 648, 680, 620 and 635, heat to 200°C+. Always use proper bearing extraction tools — never knock a bearing out cold from a Loctite-bonded housing.
Can Loctite retaining compound be used on keyways?
Yes — retaining compound can supplement a keyed assembly, particularly where fretting corrosion between key and keyway is a problem. Apply compound to the key and keyway surfaces before assembly. This prevents the fretting that causes keyway wear in high-vibration drives.
Is Loctite retaining compound the same as Loctite 603?
603 is an older Loctite retaining compound grade that has largely been superseded by 609 and 641 in the current Loctite range. If you have a specification that calls for 603, confirm with Loctite or AIMS that 609 or 641 is the appropriate current equivalent.
Can Loctite retaining compound be used on bearings with shields or seals?
Exercise caution. The compound should contact the bearing OD and housing bore, not the bearing internals or seals. Squeeze-out that contacts rubber seals can cause seal degradation. Apply the compound to the housing bore rather than the bearing OD where possible, and clean up squeeze-out immediately before it cures.
How strong is Loctite retaining compound vs press fit?
This depends on the press fit specification and the compound grade. A correctly specified H7/p6 interference fit on a 50 mm shaft generates a retention force significantly higher than retaining compound alone. Retaining compound used as the sole retention method is appropriate for light to moderate loads — check engineering calculations. For high-load applications, retaining compound plus an interference fit is the correct design.
What is the shelf life of Loctite retaining compound?
Typically 24 months from manufacture when stored at 8–21°C in original sealed containers, away from direct sunlight. Exposure to heat accelerates decomposition. If the product has thickened significantly or changed colour from the expected amber/yellow, discard and replace. Always check the label for the specific grade's shelf life and batch date.
What is Loctite 620 retaining compound used for?
620 is the high-temperature grade in the range, rated to 230°C — used where 638, 648 or 680's 180°C ceiling isn't enough. Typical applications include locating pins in radiator and heat-exchanger assemblies, sleeves in pump housings running hot, and bearings in automotive transmissions and other elevated-temperature drivetrain components.
What is Loctite 635 retaining compound used for?
635 is used where maximum bond strength on a cylindrical fit is the priority — Loctite positions it as the strongest grade in the retaining compound range. It fixtures in 6 minutes, fills the gap between mating surfaces up to 0.15 mm diametral clearance, and is chosen over 638 or 648 when their faster 3–4 minute working window is too tight for the assembly in hand.
People Also Ask — Loctite Retaining Compound
Q: What is Loctite retaining compound made of?
It's an anaerobic acrylic adhesive — a resin system that stays liquid in the presence of air but cures to a hard, solid bond when confined between close-fitting metal parts with no oxygen present.
Q: How long does Loctite retaining compound take to fully cure?
Handling strength arrives in minutes (3–20 depending on grade), but full rated strength across all grades requires 24 hours at 22°C. Below 10°C, allow considerably longer — as with threadlockers and thread sealants, cold conditions slow anaerobic cure significantly.
Q: Where to buy Loctite retaining compound in Australia?
AIMS Industrial stocks the full Loctite retaining compound range — 609, 620, 635, 638, 641, 648, 660 and 680 — with same-day dispatch across Australia.
Q: Can retaining compound replace a bearing fit entirely?
For light to moderate loads, yes — retaining compound alone can be the specified retention method. For high-load or high-shock applications, engineering practice is to combine it with a press fit rather than rely on adhesive alone; check the application's engineering calculations before deciding.
Related Guides
- The Complete Loctite Application Guide — overview of all Loctite product families including threadlockers and thread sealants
- Loctite Threadlocker Guide — for locking bearing fasteners and housing bolts
- Loctite Thread Sealant Guide — for sealing hydraulic and pipe connections in bearing-lubrication systems
All technical specifications should be verified against the current Loctite Technical Data Sheet for the specific product grade before use in engineering or safety-critical applications. Contact the AIMS Industrial team if you need help specifying the right retaining compound for your application.