Its a 4 bar under the square, but the very edge of the square is where the cleaning stops. Unlike the round ones, which are about 1-2" in from the edge.
No someone local does these for us. I forgot to add that sinice it is square the water has a place to exit ( the corners ), thus less vacuum.
The 16" ones really kill, they rip out weeds and grass with no problem.
It definitely keeps you cooler, I kept bumping in to things with it at first. I put it to good use today, The sun was beaming. I had a real nice Mexican man offer me 10 bucks for it, I told him he probably wasn't aware that this was a reef original and it would cost him $20. He looked at me like I was crazy and walked off, some people!