Twist-lock style connector for a 4-inch dust hose. The 'a' part is sized to fit a 4-inch blast gate (the aluminum gates that I happen to have). The 'b' part is sized to be clamped to the end of a 4-inch flex hose, and fits inside of 'a' and twists to lock in. The ribs on 'b' help firmly grab the dust hose when clamped on with a hose clamp.
Print with supports for the cutouts on 'a' and the nubs on 'b'. I printed 'b' with the nubs towards the bottom so that the supports did not need to be very tall.
Designed in Fusion 360 - and the export is attached if you wish to customize.
I printed with 4 walls, which effectively made these solid.