I need the smallest down rod possible for my Hampton Bay ceiling fan. Please tell what the smallest available size is and how do I order? Mine it threaded on the one end with 2 pin holes.

I found a page with downrod replacements. Not Hampton Bay though. You may need to find one which is universal. Hampton Bay parts are harder to find. They are the store brand of Home Depot only. Try talking to Home Depot - you won't find them anywhere else. Very much doubtful. If you do let us know

Here is that link I don't know how helpful it'll be as no Hampton Bay parts are there.

Ceiling Fan Downrods, Downrod replacements (http://www.ceiling-fans-n-more.com/ceiling-fan-downrods.php)

Go to Home Depot or Lowe's, they have loads of rods, all the same as yours, starting at 4"