This is probably wrong and you will probably kick my ar$e for it, but I need to know. I replaced the plastic flex pipe on my dryer with a metal one (as is recommended here). The tube is 4 inches in diameter but the dryer vent in the wall of my 50 year old house is 3 inches. So I have used a reducer to reduce from 4 inches to the 3 inch vent. I have not used screws. I know it’s wrong, but what can I do? And would you call it?
If it was a tapered transition, which I doubt, it wouldn’t be as bad as a squared off 4" to 3" reducer. Good potential for lint build up. But the bottom line is it was designed for a 4" exhaust so I’d fix it by cutting the hole in the wall bigger and installing the proper 4" one.
You cant use screws in a dryer vent. I wouldnt call it.