If you've ever put anything together that uses nuts and bolts, you know that within a few weeks you could usually count on seeing the bolts loosen a bit. The loosening is generally due to vibration; as the appliance or machine vibrates, the bolts move very subtly. The bolts are threaded, and it would be difficult for the bolt to turn in the direction that would make it tighter. So, as it moves, it moves in the direction that would make it eventually loosen. Unfortunately, this can make the appliance or machine difficult--if not dangerous--to use. So, here are three easy ways to keep bolts in their place.
Use a Jam Nut
If the shaft of the bolt is long enough, try fitting a jam nut in between the regular nut and the machine or appliance parts. A jam nut is about half the size of the regular nut. When you use a jam nut, you're adding an additional surface that's snug against the bolt threads but that rests against those threads in a slightly different way.
In a basic jam nut setup, you tighten the small bolt, and then tighten the regular bolt so much that the jam nut is, as the name suggests, jammed against the appliance's surface. This has the odd effect of making the threads of the bolt rest against one of the flanks (a flank in a nut is the side of the groove into which the bolt threads fit, so nuts have a few top and bottom flanks) of one nut, and the opposite flanks of the other nut. For example, the threads would rest against the top flank of one nut and the bottom flank of the other. This difference makes it more difficult for the bolt to move easily, if at all, due to vibration.
The advantage to using a jam nut is that it's easy. One nut is all you need per bolt. The disadvantage is that there is still the potential for the bolt to loosen if vibration becomes quite bad.
If you really want the bolt to stay in place, special sealants are available that will make the bolt pretty much permanent. The advantage to this tactic is, of course, that the bolt isn't going anywhere. However, the disadvantage is also that the bolt isn't going anywhere if the appliance is something you need to dismantle. You could damage the threads of the bolt if you try to force the glue out from between the bolt and the nut. Before using a permanent solution, talk with a professional, like McFadden-Dale Industrial Hardware, to see if they have any other tips.
Use an Anti-Vibration Nut or Lock Washer
If you're open to replacing the nut in the bolt-nut pair, special nuts are available that have rubber or nylon inserts which dampen vibrations. You can also find washers with similar features if you want to keep using the original nut. As with jam nuts, there's the potential for these to fail if the vibration becomes too strong. There's also the issue of degrading rubber or nylon as the nut or washer ages.
If you'd like to see more ways to keep bolts from loosening, talk to a tool manufacturer or a hardware store. There are several solutions that range from simple to advanced, and the staff you speak with can help you find the right part for your home appliances.