Promolyze
Loctite Threadlocker Blue 242

Auto & Tools · Loctite Threadlocker

Loctite Threadlocker Blue 242

Stop bolts backing out under vibration — without making them permanent.

  • Medium-strength hold: resists vibration, removable with hand tools.
  • Designed for metal fasteners roughly 1/4" to 3/4" in diameter.
  • A drop per fastener — one small tube lasts years in a toolbox.

$6.31

On Amazon when we checked (June 16, 2026) — live price may differ.

See price on Amazon

By Patrick Smith · Updated July 11, 2026 · How we review · We may earn a commission from Amazon links.

Price when checked
$6.31
on Amazon, June 16, 2026
Best for
Best for automotive, mower, bike and household bolts subject to vibration; not the right…
Biggest complaint
The recurring caveat is surface prep: 242 needs clean, oil-free threads to cure, and forum users note the 243…

Our verdict

The default choice for any metal fastener you want to stay put but might remove later. If you can't fully degrease the threads, buy 243 instead.

Reasons to buy

  • Users treat blue Loctite as the standard fix for fasteners that back out, praising how reliably a single drop holds through vibration and how long one tube lasts.

Reasons to skip

  • The recurring caveat is surface prep: 242 needs clean, oil-free threads to cure, and forum users note the 243 successor works on lightly oily hardware — several also warn against over-applying, which leaves messy hardened residue.

Loctite Blue 242 solves a specific problem: bolts and screws that vibration slowly backs out. A single drop on the threads cures into a plastic-like lock once the fastener is tightened — strong enough to hold through engine and equipment vibration, yet still removable with ordinary hand tools, which is the whole difference between blue and the permanent red grades. Two things trip up first-time users. The threads must be clean and oil-free for 242 to cure properly; the newer 243 formula tolerates light oil contamination, which is why some mechanics have switched to it. And less is more — flooding a fastener just leaves hardened residue to scrape off. The tiny tube looks expensive per ounce until you realize each job uses a drop and it lives in a toolbox for years.

What buyers say

Our summary of recurring themes in customer reviews on the Loctite Threadlocker Blue 242 Amazon listing (read July 2026) — not quotes or endorsements.

Most praised

Users treat blue Loctite as the standard fix for fasteners that back out, praising how reliably a single drop holds through vibration and how long one tube lasts.

Most common complaint

The recurring caveat is surface prep: 242 needs clean, oil-free threads to cure, and forum users note the 243 successor works on lightly oily hardware — several also warn against over-applying, which leaves messy hardened residue.

Worked best for

Best for automotive, mower, bike and household bolts subject to vibration; not the right pick for oily threads or plastic parts.

Frequently asked questions

Can I remove a bolt treated with Loctite 242?

Yes — that's the point of the blue grade. It is rated as medium strength, so fasteners break loose with ordinary hand tools. Red threadlocker is the permanent grade that typically needs heat to release.

What's the difference between Loctite 242 and 243?

Both are medium-strength blue threadlockers. 243 is the newer formulation with better tolerance of slightly oily threads and higher temperature resistance; 242 wants clean, degreased threads. Forum users report using them interchangeably on clean hardware.

How much should I apply?

One drop onto the engaged threads is enough for most fasteners. Applying more doesn't add holding power — it just squeezes out and hardens into residue around the joint.

Loctite Threadlocker Blue 242

$6.31 on Amazon when we checked (June 16, 2026). Amazon handles checkout, shipping and returns.

See price on Amazon →

More in Auto & Tools

Related products we track in this category