I moved my coffee roasting station but kept my blower in the same place (less noise!) so that meant I needed to extend the fume hood’s vent line. I went the cheap route and got a 10′ long piece of HDPE Triplewall pipe which cost about $7.60 at my local Home depot. Its inner diameter is around 4″, and I use ducting that also has a 4″ inner diameter so an adapter was needed. One trick is to cut off a short length of pipe, say 3″‘, and cut out enough of its circumference so that it fits inside its parental pipe. This gives you a male end for your female duct hose.
Through the power of high school math and a pair of digital calipers I determined the required circumference removal to be 31mm. I use metric for computed figures because applying them back to the work is easy. My cuts/measurements weren’t perfect as you can see but I simply taped over the gap with a bit of aluminum HVAC tape. The adapter was primed/glued in with standard PVC bonding products (i.e. purple primer and cement).
My 4″ ducting hose fit perfectly over the DIY adapter.