It's a bit hard to tell from the pics, but from photo keg34 it looks like a 1-1/2 triclamp.
This is a handy reference to determine sizes: http://www.gvc.net/docs/gvc_doc_00004.pdf
1" and 1-1/2" triclamp fittings use the same clamp. The gaskets are different though as you'll notice in the link above.
Here's another good reference with some pics of 1" and 1-1/2" ferrules. If you measure the flange and the pipe ID/OD you should be able to figure out what size you have.