While I was planning a new Selkirk DSP double wall pipe system for a wood stove, the most common confusion I found with these is the crimp that you can see from the outside goes up...but there's a crimp on the inside wall that goes down, which you cannot see in stock photos. I never found a good pic of this system before I bought it so I thought I'd share some pics for others looking into this pipe. The first image shows the end that goes towards the stove, with the inside wall crimped. The single crimped end in the second pic goes towards the chimney and fits over the inside wall crimp.
I also wanted to warn any potential Selkirk DSP customers that the 45 degree elbows are in fact NOT adjustable, which is still how they are advertised on many websites (including where I bought them, NorthlineExpress, (broken link removed to http://www.northlineexpress.com/chimney/chimney-pipe-stove-pipe/stove-pipe/6-inch-black-stove-pipe/6-inch-dsp-stove-pipe/6-dsp-double-wall-45-degree-elbow-dsp-6e4-dsp-6e4.html)). If I didn't have an existing Selkirk chimney, I definitely would have went with another brand.
I also wanted to warn any potential Selkirk DSP customers that the 45 degree elbows are in fact NOT adjustable, which is still how they are advertised on many websites (including where I bought them, NorthlineExpress, (broken link removed to http://www.northlineexpress.com/chimney/chimney-pipe-stove-pipe/stove-pipe/6-inch-black-stove-pipe/6-inch-dsp-stove-pipe/6-dsp-double-wall-45-degree-elbow-dsp-6e4-dsp-6e4.html)). If I didn't have an existing Selkirk chimney, I definitely would have went with another brand.