I buy 3/4" alum. tubing from Lowe's for the outlet tubes, I use a pc. of 1-1/2" x 1-1/2" alum. square that you can buy at any glass place that installs "store front" type windows/doors, I make a 1/4" thick or whatever thickness needed to clear the side of the engine cooling fins, and use thickwall alum. ferrells inside to keep the square tubing from collapsing(?) ; cap off the end of the sq. tubing and you're done......works for me........