DIY Self-Locking Nut

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Introduction: DIY Self-Locking Nut

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

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92 Comments

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

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?

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.