I've been shooting ARs for decades but I only just discovered that the GI cleaning kit is not the same thread as the typical gun cleaning rods.

I got a chamber brush somewhere that would not fit my cleaning rod. I tested the brush with the GI cleaning kit in the buttstock of my AR (which I never used) and it fit.

Why is the GI cleaning kit a different thread? I don't remember where I got that chamber brush but I don't remember it having a different label.

But I got a new chamber brush that does fit my cleaning rod and it says "8/32".

Anyone know why the GI kit is different?

The rods have a substantial counterbore, probably to keep dummies from breaking the brush off at the thread.

Somebody makes an adapter for the USGI rod to take standard brushes.

They make adapters to go each direction with the both thread brushes. I also know for a fact when the worn brush is taken off the adapters comes off with it and gets thrown away with the old brush.

The adapter that I use the most takes the standard thread brush and adapts it to the military thread  T handle.  It is so I can use a 308 chamber brush and  a 7.62 x39 chamber brush with the handle.

What is the "GI Thread" if not 8-32? 8-36"?

It is kind of an 8-36. It has the thread portion then an unthreaded rebated portion that is not thread that screws into the rod. I would guess to strengthen the attachment between the two. I have had normal section just threaded brass and aluminum rods that broken off at the threads after time and use.

I believe it was made that way to push objects out of the bore.

In WW2 the garand was issued with a pull string that would break and get stuck in the barrel. Also when soldiers got into the field, sometimes mud or something gets stuck in the bore and they have no way to remove it.

So the extra length, I believe secures it a little better so one can push out any sort of obstruction.

Especially, if the threads are loose.