"dean" wrote in message

Down from dryer in flexi metal 4" pipe. Along a series of 2' long
galvanized sheet metal ducts held together with screws that stick
through to the inside of the pipe (catching lint?), through a 90 and
then out through the wall and a plastic louvred vent under a wooden
deck. Ducting to be strapped directly touching the floor joists with
metal strapping nailed to joists.

Ok?

No, not OK, but close.

Dryer vents should not have sheet metal screws for the reason you mention..
Fit the galvanized together and tape them and you should be OK.