I wanted a super powerful inline duct fan for exhaust for my laser cutter, so I got the Cloudline S8. This is an adapter to reduce from 8" to fit 6" ducting.
https://www.amazon.com/AC-Infinity-CLOUDLINE-S8-Controller/dp/B07J9PTYRN/ref=sr_1_3?crid=1BWSQG7EKXGCD&keywords=8+in+cloudline&qid=1662904984&sprefix=8+in+cloudlin%2Caps%2C136&sr=8-3&ufe=app_do%3Aamzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0