[Drair]

The red pen in this picture is pointing to the nut for the through-bolt holding my backrest to the seat bracket. It has indented rectangles on every other of the six sides. Does that mean something important, or is it just from the production process, for some assembly reason?

It goes on hard, almost like it's the wrong size thread for the bolt (but it is not). Inquiring minds...

 

[Zee Fifty]

It sounds like it’s a locking nut. The dimple is the manufacturing process used to deform the threads slightly.

 

[DDL]

You are correct.....

It sounds like it’s a locking nut. The dimple is the manufacturing process used to deform the threads slightly.

That is one of the methods for making a self locking nut. It generally is not that common, but it is effective. The nylon locks are more common; but with many off and on cycles, it will eventually wear to the point it no longer functions as a self locking nut. Another method is with a metal disk formed into the outer end of the nut (see shock and shock linkage nuts for a sample). These do not have the eventual wear issue of nylon as well as being heat tolerant. Another type of self locking nut has a flared base with "one way" ridges that bite into what it is next to like a lock washer.

 

[weengers]

You are a very sound sleeper!

 

[tamathumper]

That's a self-locking nut, as others have said. If it came off your Utopia backrest I'll bet you have the same issue as me - you can snug it up and the backrest will stay in place for a while, but soon the backrest will be loose and flopping forward again.

 

[cihilb]

Try inserting the bolt from the other side of the backrest. When the nut is on the left side, it wants to loosen everytime you push the backrest forward. You can also try double nutting the bolt and tighten the outer nut into the inner. Nylon washers may also help.

 

[tamathumper]

Try inserting the bolt from the other side of the backrest. When the nut is on the left side, it wants to loosen everytime you push the backrest forward. You can also try double nutting the bolt and tighten the outer nut into the inner. Nylon washers may also help.

I'll try that right now, thanks.

 

[Farmguy]

And/Or go to a home depot or lowes (or wherever is nearby that has a suitable selection) and get a new 'nyloc' or other locking nut.