Well, let's see,they are both either males or females.
I'm going to guess they're both females, so you would need a short coupler w/ both ends crimped into male ends.
If it is the other, you guessed it, you need a short piece of straight stove pipe to accept the 2 males.
Sheet-metal shops have a hand cranked or machine to roll the pipe and crimp it into a male end. You may want to enlist them for help...the stainless is a little tougher than the steel, but still easily done w/ the machine/crank.