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What is a Threadlocker?

By R. Kayne
Updated May 17, 2024
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"Threadlocker" is a general term that refers to a liquid polymer that is designed to be brushed onto the thread of fasteners, such as screws, just before they are installed. The polymer dries and locks the fasteners in place, protecting the threads against water, rust and leakage. Threadlockers are especially useful in the assembly of moving parts, engines, hobby toys and plumbing applications in which, for example, a loose gasket screw can result in water damage.

Purposes and Formulas

There are several types of threadlockers that are designed to be used for different purposes. Large screws, bolts, bushings and studs require strong formulas of threadlockers. Some manufacturers of these formulas color-code their products by category to make shopping easier. For example, a heavy-duty formula might have a red color-coding on its packaging, and light-duty formulas might be purple or blue.

Any type of threadlocker usually has had its holding power tested and rated. This is recorded and reported in either pounds per square inch (PSI) or kilograms per centimeter (kg/cm2), which represents the force that must be exerted to "unlock" the threadlocker so that the fastener can be removed. A heavy-duty threadlocker that is used to assemble engine parts such as rocker arms, shock absorber bolts or frame bolts might be rated at 3,000 PSI (about 210 kg/cm2). There also are medium-grade and light-duty formulas for fasteners as small as computer screws.

Types of Threadlockers

Threadlockers can come in permanent or removable blends. Fasteners that have been installed with a permanent threadlocker applied might require heat or power tools for removal. The instructions that come with a permanent formula typically tell the user how to remove a fastener that has had the threadlocker applied. Parts that have been assembled with removable threadlockers usually can be disassembled with hand tools and a little effort.

Pre-assembled materials such as carburetors, instrumentation, or electrical connectors commonly use wicking-grade threadlockers. These formulas gradually penetrate to seal and protect welded seams or porous metals. Wicking-grade threadlockers also require heat for removal.

A threadlocker can be an essential item to have for everyday home repair needs. Whether used for plumbing bushings, car or motorcycle repair, toys, electronics or another use, a threadlocker can come in handy many times. This product generally comes in small bottles in amounts of 8.5 fluid ounces (about 250 ml) or less. It is available at automotive, hardware, plumbing and home improvement centers. Some larger grocery chains might also stock light-duty formulas.

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Discussion Comments
By truman12 — On Jul 07, 2011

@Ivan83 - Yeah I agree. I work in an auto shop and we use thread sealer all the time, but not just to work on cars. I've seen guys put it on fishing lures and pool equipment. We also of course, use it on all kinds of stuff when we are working on cars. It really is magical stuff.

I've seen a few jobs when people failed to use it and the results can really be disastrous. It really speeds up the wear and tear and there is almost no excuse for not using it. A good mechanic will have some at hand when they are doing any job.

By Ivan83 — On Jul 06, 2011

Just like the article says, thread locker is really important to have in any home or toolbox. The uses of it are really too many to list. I've used it when working on plumbing and electric, when I'm working on my car, when I'm fixing my kids toys and even once when I was fixing my glasses. I love this stuff. Definitely keep some around your own home.

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