Blue 242 is the default name in medium-strength threadlockers, competing with Permatex Medium Strength Blue 24200, Vibra-Tite 122, and its own successor Loctite 243 (oil-tolerant, no primer needed on inactive metals). On Amazon it holds Amazon's Choice in the thread-lock category with 10K+ monthly purchases, surrounded by sub-$10 generic clones (ESKONKE, EPASUN) trading on the '242/243' numbering.
By [AUTHOR NAME]·Owned, in use·4.8 across 43,267 ratings (verified 2026-08-31; normal buy box, sold and shipped by Amazon.com, single 6 ml tube, Amazon's Choice, 10K+ bought in past month) on Amazon
Published: [DATE]Listing re-checked: Aug 31, 2026My measurements: pending
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The verdict
Direct answer: Loctite Threadlocker Blue 242 is a medium-strength anaerobic threadlocker for 1/4"-3/4" metal fasteners that sets in about 10 minutes, fully cures in 24 hours, holds 70-150 lb-in breakaway torque on 3/8-16 steel across a -65°F to 300°F service range, and releases with ordinary hand tools - but Henkel's own data sheet requires a primer on inactive metals like zinc-plated or black-oxide fasteners, the gap the newer 243 formula was built to close.
Owned & in use
Loctite Threadlocker Blue 242
For: Anyone with fasteners that vibrate loose - mowers, bicycles, motorcycles, cars, power equipment, furniture hardware - who wants them locked but still removable with hand tools later.
Skip if: You're working on or near plastic parts, or locking stainless/plated fasteners without primer - buy Loctite 243 instead; and if you ever want the joint permanent, that's red 271, not blue.
Owner photos & measurements coming
I own this one — my photos and hands-on measurements land in the next update to this page. Until then, every claim below is sourced and linked; nothing is invented.
Key specs
Spec
Value
Strength grade
Medium - removable with standard hand tools
Fastener size range
1/4" to 3/4" (6-19 mm) metal fasteners
Set / full cure time
~10 minutes on steel (longer on less active metals); full cure 24 hours
Breakaway torque (24 h)
70-150 lb·in on 3/8-16 steel nuts and bolts (ISO 10964)
Service temperature
-65°F to 300°F (-54°C to 149°C)
Chemistry
Dimethacrylate ester, anaerobic cure (cures in absence of air between close-fitting metal)
Package size
0.20 fl oz (6 mL) carded squeeze tube
Shelf life
24 months from manufacture, unopened; not damaged by freezing
What independent testing and the community found
Henkel Technical Data Sheet (Oct 2024 revision) — Documents the torque, cure, and temperature numbers, ~100% strength retention after 500 hours in motor oil/gasoline/brake fluid, and the limitations: primer needed when both metals are inactive (plated, black-oxide), and not for use on plastic parts due to stress-cracking risk.
Chief Delphi (FIRST Robotics forum) - Loctite-on-polycarbonate testing — A robotics team ran a multi-week coupon test of blue threadlocker in contact with polycarbonate: most exposed coupons crazed, tore, or fractured when bent (one showed tearing at 2.5 hours), empirically confirming the TDS warning to keep it off plastics.
MTBR (Mountain Bike Reviews) forum thread on Loctite 242 — Cyclists report it works as advertised with no heat needed for removal and that a small bottle 'lasts forever' on bike work; members also note 242 has been discontinued in some regions and replaced by the primerless 243.
Loctite official product page (Threadlocker Blue) — Manufacturer's consumer-facing claims: sets in 10 minutes, cures in 24 hours, for 6-19 mm fasteners, removable with hand tools, prevents vibration loosening on small motors, mowers, and power equipment.
Pros and cons
What works
Cured joints come apart with ordinary hand tools - Henkel's data sheet reserves heat (approximately 482°F) only for rare cases of excessive thread engagement.
Performance is unusually well documented for a $7 tube: 70-150 lb-in breakaway torque on 3/8-16 steel after 24 hours, service from -65°F to 300°F, and testing to Mil-S-46163A and ASTM D5363.
Henkel's aging data shows roughly 100% strength retention after 500 hours immersed in motor oil, gasoline, and brake fluid, which is why it holds up on valve covers, water pumps, and mower decks.
A few drops treat one fastener, so the 6 ml tube covers dozens of jobs - forum users on MTBR describe a small bottle lasting years of bike maintenance.
What doesn't
Henkel's own TDS says inactive metals (zinc-plated, cadmium, black-oxide, and similar) need a Loctite primer for a proper cure - the newer 243 cures primerless and tolerates light oil, and 242 has been discontinued in favor of 243 in some regions.
Never use it on or near plastics: the TDS warns of stress cracking, and an independent FIRST Robotics team test on Chief Delphi documented polycarbonate crazing and tearing after exposure.
Recurring Amazon and Home Depot complaint families: tubes and bottles arriving partially empty (headspace is actually by design for anaerobic adhesives, but it reads as shorting), dried-out or clogged dispensing tips on older stock, and occasional off-consistency batches.
243 is Henkel's newer medium-strength formula: it cures without primer on inactive metals like stainless and zinc-plated fasteners and tolerates lightly oily threads. 242 works fine on clean, active steel. If you're not sure what metal you have, 243 is the safer default; some regions have discontinued 242 entirely in its favor.
Can I remove Loctite Blue 242 without heat?
Yes - that's its defining feature. Medium-strength blue is designed to release with standard hand tools. Henkel's data sheet says only rare cases of excessive engagement length need localized heat to about 482°F before disassembly.
Does Loctite 242 work on plastic?
No. The technical data sheet explicitly warns against plastic parts because thermoplastics can stress-crack, and independent testing by a robotics team showed polycarbonate crazing and tearing after contact. For plastic-adjacent fasteners, Loctite makes 425, a plastic-safe alternative.