I was running entirely flex hose to three machines (jointer/planer, table saw and band saw), I am switching to mostly (4") metal ducting and using small runs of flex hose between that and the dust collector and the three machines. My question is about connecting the flex hose to the metal ducting, I am using those connectors that are about 6" long and crimped at both ends. The first one I used self-tapping screws (1/2" the shortest I could find) to secure a connector the the metal ducting at each end, now I have these screws sticking out almost half an inch into my ducting for the jointer, not sure if that is really a problem or if the little that it does restrict air flow is too small to worry about. For the other two pieces of ducting, they are not connected to flex hose yet, I just hammered a connector into each end of the other two pieces, they are in there really snugly, is this enough? Is there any reason to fix the connectors to the inside of the ducting using some sort of fasteners/adhesive? I also wrap that aluminum tape around the end of the ducting and onto the connector pieces.