12 6” blast gates. Things nut & bolted together, tighten to make slider snug yet loose. Added detent with ball bearing and spring for open & close. Added spring latch for dust/chipping escape when slider is closed. Next, covering detent spring, re-adjusting entire 6” HVAC to add in these blast gates through the main line and at the ends.
-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"