metal
What's the name of the "circle" that the arrow points to?
In the picture is the end of a barbell. That thing that arrow points to is put onto the tube. The tube has a "dent" where that circle fits. There are eyes in the end of the circle that are used to expand it slightly so it can move easily onto the tube and when it's in the dent, it's released so it clasps.
It may be that the frame was originally designed to have slats span the rails, and not have the mattress (box spring) sit directly on the rails. This would have lifted the mattress up a bit, and possibly allowed it to ride over the bits that are giving you trouble.
This was one persons solution:
I live in a "high wind area" and you don't need to go with deeper holes.
I think your 30" depth is adequate and the size of the hole is more than adequate for a 6' fence. The problem is that you need to pour a concrete "collar" at the top of the hole.
I guess you could fill the post hole up with concrete, but you have rather large holes and that could be expensive. I'd dig out the dirt backfill down to the concrete at the bottom of the hole. (I'm assuming the metal fence post is partially encased in the concrete at the bottom of the post hole.) Then, I'd fill the hole up with crushed rock to the point that about 1 bag of concrete would fill the balance of the hole...creating a collar at the top of the post hole.
Best Answer
That is called a "circlip" and can be removed or positioned with special pliers made for them. They come in internal and external varieties. What you have pictured are internal. Some circlip pliers are reversible (the ones in the picture) so you can use them with internal or external circlips.