Threadlocker is a general term for a liquid polymer designed to brush on fastener threads just prior to installation. Threadlocker dries and locks fasteners in place, protecting the threads against water, rust, and leakage. It is especially useful in the assembly of moving parts, engines, hobby toys, and plumbing applications where, for example, a loose gasket screw can result in water damage.

There are several different types of threadlocker designed for different jobs. Large screws, bolts, bushings and studs require strong formulas. This type of threadlocker normally rates its holding power by pounds per square inch, or PSI. A heavy-duty threadlocker such as that used to assemble engine parts like rocker arms, shock absorber bolts, or frame bolts might be rated at 3,000 PSI. There are also medium grade and light-duty threadlocker formulas for fasteners as small as computer screws.

Threadlocker also comes in "permanent" and "removable" blends. Fasteners installed with permanent threadlocker might require heat or power tools for removal. Read the manufacturer's packaging for instructions. Parts assembled with removable threadlocker can be disassembled with hand tools and elbow grease.

Some top manufacturers of threadlocker color-code their products by category to make shopping easier. For example, heavy-duty threadlocker might be red, while light-duty formulas might be purple or blue. Pre-assembled materials such as carburetors, instrumentation, or electrical connectors commonly use wicking grade threadlocker. Wicking grade threadlocker gradually penetrates to seal and protect welded seams or porous metals. This type of threadlocker also requires heat for removal.

Threadlocker is an essential item to have around the house for everyday home repair needs. Whether used for plumbing bushings, car or motorcycle repair, the RV, hobby planes, toys, or electronics, threadlocker can come in handy again and again. This product generally comes in small bottles in amounts from 5 - 250 milliliters (about 1 teaspoon to 8.5 fluid ounces). It is available at automotive, hardware, plumbing, and home improvement centers. Some larger grocery chains might also stock light-duty blends.