This box spring is GREAT!  We ordered for our king sized mattress. When we received the package, I got a call from my husband saying I must have ordered the wrong thing the packaging was way too small. I went back and checked my order and then read the reviews.  Turns our the packaging is simply genius.  The two box springs are twin sized, folded in half and flattened.  When you open them they turn into real box springs.  Great price and shipping was fast, sturdy product!  I'm not sure the difference in box springs, I just know this one did exactly what we needed.