The International Cessna^® 170 Association

Those parts look like U bolts. Get ahold of a "McMaster-Carr" catalog: thay have every size and type U bolt made. Just be damn sure you don't let them know it is for an airplane!

I have the Pat Bartone pipes. The hangers are fabricated from doubled .035 SS sheet for the top hanger and aluminum angle for the bottom hanger, joined with a piece "Aircraft grade" tire sidewall. These have worked great for 31 years.