Blue 242 is the default name in medium-strength threadlockers. Its rivals are Permatex Medium Strength Blue 24200, Vibra-Tite 122, and Loctite's own successor, 243, which needs no primer on plated metal and tolerates a little oil. It is the tube everyone buys first, which is why the generic ones (ESKONKE, EPASUN) borrow the 242/243 numbers. Mine has held a pocket-knife screw and a fishing magnet.
By Mendy·Bought at retail
Published: Aug 31, 2026Listing re-checked: Aug 31, 2026Updated: Sep 30, 2026
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The verdict
Direct answer: Buy it for any metal fastener you want to stay put and still get off later with hand tools. Loctite Threadlocker Blue 242 is a medium-strength anaerobic threadlocker for 1/4" to 3/4" metal fasteners. It sets in about 10 minutes and fully cures in 24 hours. Henkel rates it at 70 to 150 lb-in breakaway torque on 3/8-16 steel, from -65°F to 300°F. The one gap: Henkel's own data sheet wants a primer on inactive metals like zinc-plated or black-oxide fasteners. The newer 243 was built to close it. I bought mine at retail. It has held a pocket-knife screw I had backed off to free the blade, and the screw on my fishing magnet, the one job where a loose screw means hauling up an empty rope. When I needed a screw back out, a screwdriver and some elbow grease did it.
Bought at retail
Loctite Threadlocker Blue 242
For: Fasteners that vibrate loose: mowers, bicycles, motorcycles, cars, power equipment, furniture hardware. You want them locked, and you want them off again with hand tools later.
Skip if: You're locking stainless or plated fasteners and don't want to buy primer too: get Loctite 243. You want the joint permanent: that's red 271, not blue. And it stays off plastic parts, per Henkel's own data sheet.
On a pocket knife. I actually used it on a pocket knife. It may have been my small Spyderco Lil' Native. I needed to loosen the screw, since the blade was not smoothly opening and closing, but I didn't want it to get any looser. The screw was tight, but when I loosened it, it seemed like it was going to come out on its own. I didn't want it slowly loosening over time, so I got the Loctite.
On a fishing magnet. I also used it on my magnet for magnet fishing. The screw in the magnet was loosening, and I do not want to keep pulling the magnet line and then find nothing attached, so I got threadlocker for that as well. The magnet fishing set came with threadlocker. I didn't need it for a while, but once that dried up I needed to get more.
Getting it loose again. I did not have to use any tools besides my hands and a screwdriver. It wasn't easy, but I was able to get it done with some elbow grease.
Near plastic. I did not notice anything in particular. Definitely nothing to be concerned about in small volumes, in my opinion.
Plated or stainless bolts. I haven't seen any issues with this, but if you are using it for a more industrial purpose, you might want to test this on your end.
243 or red? Honestly, I never found the need for it. 242 seemed to do the job for the basic around-the-house use cases.
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 the testers and the forums found
Henkel Technical Data Sheet (Oct 2024 revision) — The source for the torque, cure and temperature numbers. It also reports about 100% strength retention after 500 hours in motor oil, gasoline and brake fluid. The limits are on the same sheet: a primer when both metals are inactive (plated, black-oxide), and no plastic parts, because of stress cracking.
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, and one showed tearing at 2.5 hours. That is the data sheet's plastic warning, confirmed on a bench.
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) — The maker's consumer-facing claims: sets in 10 minutes, cures in 24 hours, for 6 to 19 mm fasteners, removable with hand tools. The jobs it names are 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 (about 482°F) for rare cases of excessive thread engagement. Mine came apart with a screwdriver and some elbow grease.
The numbers are unusually well documented for a small consumable: 70 to 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. That 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. MTBR users describe a small bottle lasting years of bike maintenance. The tube that came with my magnet-fishing kit dried up before I got through it, which is the other way these run out.
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 without primer and tolerates light oil, and some regions have discontinued 242 in its favor.
Keep it off plastic parts. The TDS warns of stress cracking, and the FIRST Robotics team test on Chief Delphi documented polycarbonate crazing and tearing after contact.
The tube looks part-empty out of the package. That is by design: the chemistry cures without air, so the headspace is what keeps it liquid in the tube. It still reads like you got shorted. Check the date too; shelf life is 24 months from manufacture, unopened.
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.