“Righty tighty, lefty loosey”: How old were you when you first heard that? It’s the phrase our parents give us to help remember which way to turn things like faucet handles. And it applies to bolts, nuts, and other fasteners. But not to everything. And certainly not to everything in your car.
Why Some Car Parts Use Reverse Threading
Some parts are reverse-threaded. Some people call them “left-handed” screws, bolts, nuts, etc. For these parts, it’s not “righty tighty, lefty loosey” but the opposite — “lefty tighty, righty loosey” (this is just so much more fun than “clockwise” and “counter-clockwise”). And there’s good reason for it.
The most important reason for reverse threading when it comes to your car has to do with the parts of the car that move, and more specifically, turn. The torque of turning parts can gradually loosen the fasteners. Reverse the threading, and you’re applying that same torque to maintain the tightness.
Wheel lug nuts commonly use reverse threading. Putting reverse-threading lug nuts on the left wheels of the car will use the wheel-spinning torque to keep the lug nuts tight. The practice goes back to the 1930s, as engines became powerful enough for torque loosening the nuts to become an issue. In fact, reverse-threading lug nuts for the left wheels was common among American and some import brands through the middle of the last century. Conical lug nuts eventually solved the problem to the extent that most manufacturers stopped using reverse-threaded ones.
Tie rods also often use reverse threading. Again, it’s just on one side. If one side of a tie rod assembly wasn’t reverse threaded, then turning the tie rod adjuster in the middle wouldn’t change the overall length of the assembly. Turning the tie rod adjuster either shortens or lengthens the assembly, thus making it possible to align the steering properly.
How to Tell a Car Part Uses Reverse Threading
This part’s simple: Hold the fastener upright so you’re looking at the threads. They’ll appear to be slightly slanted in one direction or the other. If they appear to be going up to the right, that’s a right-handed or normal thread, so, righty tighty, lefty loosey. If they seem to be going up to the left, that’s a reverse-threaded fastener — and that’s lefty tighty, righty loosey.
Check out all the hardware available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on reverse-threaded fasteners, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
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Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of MikeHagertyCars.com, and contributes car reviews to the Los Altos Town Crier and losaltosonline.com. Previous outlets have included KFBK and KFBK.com in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and BBCCars.com.