How To Lock Nuts to Bolts
by Damien Andrews
With the advent of liquid thread lockers, do-it-yourselfers were given a marvelous alternative form of ensuring that a nut would stay in place when attached to a bolt. Prior to the introduction of liquid thread lockers, do-it-yourselfers could select from several types of lock washers, the use of a second nut, and finally self-locking nuts came along. As with everything in the shop, it's good to have choices.
Liquid thread lockers come in a couple of varieties. There's the light duty type that will allow you to simply wrench off the locked nut from the bolt. Then there's the heavy duty (permanent) type that requires either heat or the use of an impact wrench, should you ever wish to remove the nut from its host bolt. The light duty liquid thread lockers are almost always the product to use, when locking a nut to a bolt. If you believe the job calls for the use of heavy duty/permanent liquid thread locker, be pretty sure you won't want to remove the nut anytime soon.
To use liquid thread locker, simply put a drop on the threads of either the nut or the bolt. It will almost always work out to be easier to apply the drop on the bolt, but on occasion, you may find putting it on the threads inside the nut is preferable. Either method is effective. Before you put the item with the new bolt and liquid thread locked nut into service, be absolutely sure the liquid thread locker has dried. This is particularly important if the nut and bolt are installed on something which vibrates or gets hot. Liquid thread lockers do have working temperature ranges, also – so be sure to check and ensure the liquid thread locker you pick will work reliably on your particular application.
Self-locking nuts come in two basic varieties: all steel and with plastic inserts. All steel self-locking nuts require the bolt to travel through a space which is actually too small for its diameter and threads. As the bolt passes into the narrowed area of the nut, the nut holds it quite firmly, and further rotation requires tools. The self-locking nuts with plastic inserts also have a narrowed space inside the bolt, but it's made of plastic – thus allowing it to grip quite tightly to the bolt as it passes through the plastic.
Both types of self-locking nuts will allow you to hand turn them onto the bolts for the first turns – but only enough to get them started. Before the self-locking nut can become flush with the end of the bolt, you'll require wrench power for both the bolt and the nut. Once again, be sure that if you use a self-locking nut with a plastic insert on something which gets hot, you ensure that it can stand the heat and remain serviceable.
I've used both types of self-locking nuts extensively over the years. And I have to think the all steel variety is most likely stronger. With that said, I almost always use self-locking nuts with plastic inserts. They have yet to fail me, and they are ever so much easier to find in different sizes. I do make it a practice to always use all steel self-locking nuts when I do my own engine work: tractor, truck, and ATV.
Using a second nut is the old school way to secure a nut to a bolt. It is also absolutely sure fire. One big advantage to using a second nut to lock a nut onto a bolt is that you can hand turn the nuts, save for the last turn. For things that get taken apart and put back together again frequently, this can be a real time saver!
To lock a nut to a bolt using a second nut, simply turn the first nut to where you want it to be locked in place. Tighten it as necessary for its job. Now twist on a second nut until it makes firm contact with the first nut you installed on the bolt. (See Diagram 1) Now, put a wrench on the first nut, and another wrench on the second nut – the locking nut. Hold the first nut still, and tighten the second nut. You won't have to turn the second nut very far at all – less than a turn. The first nut is now locked. To remove, reverse the process: put a wrench on both nuts, twist the second nut until it is loose, then spin it off with your fingers.
If you happen to ever need to install a nut to a bolt in a situation where, no matter what, the nut cannot move or come loose – ever, then consider the following options:
- Instead of using permanent liquid thread locker, use a small amount of a permanent glue that adheres to metal. My personal favorite has always been PC-7, but I have recently grown fond of Gorilla Glue – which requires no mixing. With PC-7 I only put it where the nut will end up on the bolt. With Gorilla Glue, I put a drop at the nut's final location, and then add a drop to the exposed part of the nut, where it meets the bolt.
- Spot weld the nut to the parent bolt. Be sure the bolt is tightened to the desired foot pounds prior to doing this.
Even beginner do-it-yourselfers often have occasion to lock a nut to a bolt. It's good to know there are so many functional ways to accomplish that oft repeated task. And who knows what tomorrow's engineers will conjure up.
ProTip: If you want to ensure that a nut will never be able to be removed from the bolt it's attached to, but you still want to be able to loosen the nut and reattach it, blunt the end of the bolt. To do this, take an appropriately sized punch and place it in the center of the bolt's end AFTER INSTALLING ANY NUTS, WASHERS, ETC. Now strike the punch firmly two or three times. This will fatten the end of the bolt making it impossible to remove any nuts previously installed.