Below are two images of what im talking about. Around the duct boot for the wall register is a metal box to make up for the difference between the wall and where the trim ends. What is it called and where can i find it?
Thank you for your time.
Drywall – Metal around wall register boot for trim
drywallductsregisterwalls
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New answer thanks to updated question.
Yes, the lip around the rim of the opening I'd call it a "ridge" but I dunno if that's right) on the boot is there to help ensure a firm connection. It's to keep the zip tie on the inner core from slipping free. This is necessary (the keeping the duct snug, not nessarily the tie) if your ducting is going to be pulling away from the boot due to gravitational stresses - such as when the boot is above the duct and the duct can be pulled down, such as along a wall or below a ceiling or floor. If your boot points down and the duct sits on a horizontal surface, you're good - no extra tension should happen.
Important note - neither mastic nor tape are intended to be structural - they don't serve to hold the ductwork in place, they serve to seal the ductwork so that there are no air leaks.
So the question really is - how do I properly secure my flexible ducting to the boot when there's no lip on the collar? Answer: Self-tapping screws.
Get yourself a box of those (the hardware aisle or the ductwork aisle). When you go to mount your ducting, pull the outer insulation back up away from the core, pull the core over the collar, and use TWO screws on opposite sides of the duct (180 degrees from each other - noon and 6'o clock (or 1 and 7, 3 and 9, you get the idea) to ensure that neither side of the duct can pull free.
Use the inner to snug up the connection (don't over tighten!), seal with mastic (I'd recommend tape though cause of the insulation layer...), slide the insulation up as far as it will go and snug it up with the outer zip.
The hot attic has more latent heat (water vapor) due to both it's higher temperature and being vented to the outside. As that air mixes with the cooler interior air, relative humidity rises. When the more humid air hits the cold uninsulated duct, it condenses.
The first step is to seal the opening between the attic and the interior space to reduce convection and water vapor transfer between the attic and conditioned space. Insulating the duct would be the second step.
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Best Answer
I don't think they're made anymore, but I heard them called Register Mounts, Extensions & Collars. I looked for replacements a few times & ended up with nothing to end up wire brushing them back to bare & spray painting them, good as new.
If no-one else here answers or has an avenue to get any. You can make your own quite easily & of much better quality...in the size that you need, which might be the real problem. I'd suggest Aluminum Angle for it's workability & corrosion resistance, but you can go with steel or C-channel or J-channel.
You'd probably need about a 4' length for each one & can either attach the last corner with a tab on the inside (not on the outside like the picture) or use a corner brace with countersunk (if desired or needed) screw, bolt or pop-rivet face holes.