On Thu, 28 Feb 2013 20:17:17 -0800, "Artemus"
I've found that ones with an odd number of flutes work best.
The six fluted ones tend to make a hex shaped sink.

I bought one of these a few years back and can attest to its
effectiveness.
http://www.leevalley.com/en/hardware...=3,41306,41328