you can get those heavy duty "t-bolt" clamps from places that sell big truck and heavy equipment parts. they are about $5.00 a piece. they come in a bunch of different sizes. my friend used them to hold the 4" discharge tube on his d-3m procharger. they worked fine.
Hey Jim, If your still looking for good clamps, you should try the one's off a 2001 F350 Turbo diesel truck . I believe there 3" and are made to withstand high boost levels. Tomorrow Ill try to get a part #from my parts man. And Ill post it for anyone who's interested.
Jim, T-bolt clams are the only way to go. You can find some cheaper ones for around 3 bucks if you look around.
My only suggestion to anyone that uses them, is to take the nut off the end FIRST THING. And add a washer in there, so it aids the nuts ability to spread the load evenly. I know it's a small little detail, but it counts.