A Hartford Connecticut basement in 1953 was humble setting for the origin of something very useful. An entrepreneurial professor from Trinity College named Vernon Krieble and his son Robert, both PhD chemists developed a unique liquid resin that hardened in the absence of air. Recognizing the potential of this anaerobic sealant they patented their creation and released it to market by 1956. Starting out as The American Sealants Company, they offered one product, dubbed "Loctite," a name conceived by Robert's wife, Nancy.
Later, the company name was changed to Loctite as well and eventually became today's Henkel Loctite Corporation with distribution in countries worldwide. Over time, the range of products they offered grew as well, but for this week at least we'll concern ourselves only with their signature thread locker known, of course, as Loctite.
If you aren't familiar with Loctite, the problem it solves is that of vibration. No, not the camera shake vibration that makes it hard to get sharp images. Rather, it addresses the vibration that can cause bolts and other fasteners to work themselves loose over time. This might be from your camera bag riding in the trunk of your car as you drive down the freeway, from the repetitive motion of hiking down a trail to reach your destination in time for sunset, or simply from ordinary handling over an extended period of time. Regardless of the source, the end result is the same: things that you thought were tightly fastened together work themselves loose, often at the least convenient time.
There are three strengths of Loctite that may be of interest to photographers. Each does the same thing, but is appropriate to holding different sizes of fasteners with different degrees of permanence. Each also has its own distinctive color. They are generally available at automotive supply stores, not regular hardware stores. All three cure about 20 minutes, or to full force within 24 hours. They require metal to metal contact to work and are not effective when bonding plastic or other materials. It's best to shake the bottle before using to achieve maximum effect.
Low Strength Loctite (#222) is purple and is easily removable when needed. It is designed for fasteners up to a quarter inch in diameter and is thus relevant for only the smallest of screws generally found on photographic equipment. I've used it on the tiny screws that hold on the Kirk Enterprises modified knob for the Nikon 70-200 VR lens just to be sure it doesn't work its way loose. I've also put it on the similarly tiny screw that holds the hard drive bay in my laptop.
Medium Strength Loctite (#242) is blue is the most commonly used variety for photographic gear. It holds well but is still easily removable with hand force. Quick release plates should be easy to separate from the clamp on top of your tripod, but should be screwed on securely to your camera or lens mount foot. Blue Loctite works quite well for this.
High Strength Loctite (#271) is red and creates essentially permanent bonds. Don't use on anything you ever want to separate again. I've used red Loctite to mate a Really Right Stuff lever clamp to the top of a Markins M20-NQS ballhead.
A drop or two of Loctite can be cheap insurance against things coming loose when you don't want them to.