DIY Self-Locking Nut




Introduction: DIY Self-Locking Nut

About: I am an automation engineer but I will give anything a go. I don't know if you call if pessimism or just being an engineer, but I look for problems everywhere, then I look for some weird, left field way to s...

The humble nut and bolt, they hold the engineering world together but sometimes they won't play ball and the nut wants to spin and fall off.

There are many ways to make sure the nut stays fastened:

  • Nylock nuts
  • Anti-vibe washers
  • Spring washers
  • Thread lock (glue)
  • Double nutting (see picture)

But sometimes you may not have the normal equipment or not have space for a lock nut, this instructable will show a handy hack that will keep a nut in place while leaving the possibility to remove it with a spanner.

Step 1: The Technique

All you need is:

  • Nut and bolt
  • Electrical heat shrink
  • Heat source
  • Spanners

It should be noted that this only really works for bolts larger than M8, any smaller than that and the thread is too fine and the nut won't fit.

The idea is simple, slide heat shrink over the threaded section of the bolt

Heat it until it shrinks into the threads, also shrink the bit sticking off the end (this will act as a guide for the nut)

Push the nut down the tail of the heat shrink and start to thread it on

It will be hard to turn, much like a nylock

The nut will strip the tail and it will fall off

As you thread down, the heat shrink fills up the thread and acts as a thread lock (THIS NUT WILL NOT VIBRATE OPEN!)

If you ever need to remove it, a spanner, some brute force and ignorance will open the nut, which will clean the thread of obstruction as it goes.

Simple, quick and handy



    • Water Contest

      Water Contest
    • Fix It! Contest

      Fix It! Contest
    • Metalworking Contest

      Metalworking Contest

    92 Discussions

    I've always just used a dab of nail polish where I want the nut to stay. Way easier and faster.

    2 replies

    Yeah I've tried different kinds of paint but under vibration it normally fails. Maybe the enamel in nail polish would help thanks

    Was wondering if you had a chance to try nail polish yet and if it worked any better than regular paint.

    good idea, I use "plumbers tape" but after watching this video, I will use these washers. What to do for spark plugs?

    15 replies

    Have you ever had a spark plug come loose? I've worked on cars for 14 years and never seen a spark plug work it's way loose.

    Back around 2000, the Ford Triton 5.4 liter truck engine had only four threads for the plug to grip. They were notorious for having the plug come loose and then blow out. My truck did that at about 30 mph (50 kph?) and the plug hitting the hood was a sound I won't forget. I turned into a local repair shop and asked if someone could look at my truck. A fellow just standing there said, "You blew out a plug. I heard it when you drove in."

    Fortunately, that day it didn't ruin the engine head or the spark plug, so the mechanic just screwed it back in. It ruined the "coil pack" so I ended up around $100 for screwing the plug back in the hole.

    Thanks; that explains alot. I've never seen (I've only ever looked at MY cars) only 4 threads gripping a plug. That seems to little, especially for something 5.4 liter.

    I've seen plenty of the older aluminum heads from cheaper cars fail... Usually happens when people re-used the old spark plugs that has a hollow collapsing washer.

    Fail like how? I've never worked on a car with a cast iron head, I've never seen a spark plug come loose.

    Thanks; I read it; very helpful; covered lots of bases.

    I have been saving tips for personal use and found your link helpful - THANKS!

    I was taught in auto shop class to not reuse the compressible washers but did it dozens of times without a single failure. I'm not sure if you're talking about someone over-torquing a plug but I've never seen a plug come loose, washer or no. The washer is there for sealing, not for retention. Non-washer plugs are beveled and require a certain amount of torque that is not recommended for the older aluminum heads. I won't even get into dissimilar metal galvanic action.

    Here is a great read... if anyone is following that cares about the do's and don'ts with sparks plugs

    Spark plugs I've seen blown out of the cylinder are due to the forces of the combustion chamber overcoming the retention of what the threads should hold... or well, any of those "Don'ts" are done. It's hard to say " not causing the problem myself" what exactly happens to the cars I've had to "heli-coi"l or re-sleeve but most times I've seen more than half the threads just ripped right out and the spark plug is dangling by the wire boot or somewhere on road.

    Yes I have seen plugs come loose to the point of blowing out on the freeway. We had to keep a length of rubber hose in the glove box to replace it as it was recessed into the head. But it was a volkswagen so........

    At 75, I've done small engine maintenance since12, motorcycles from 14, and cars and trucks up to today, AND I have NEVER seen a properly installed sparkplug "back out!!!"

    You can't put something between the threads on a spark plug because the screw shell of the plug grounds the ground electrode to the engine. You also risk adding pressure to the head which could crack the head over time.

    You're 100% correct that you can't insulate the threads of a spark plug from the engine 'head' or you will have no ground connection. However, I have to somewhat disagree about the part of cracking the head. They would have to be either some *really* over-sized spark plug threads -or- some really, really crappy heads (like the GM 333882 casting 76cc heads from the 70's.. LOL). Of coarse, I'm talking about iron heads. I generally *hate* aluminum heads and try to forget they exist. =P

    If you take any metal and stuff something in between some bolts in some threads, then heat and cool it over and over, it will crack. You're putting way more stress on those threaded holes than they were designed for.