In situation like this, I like to employ the following technique to make a smooth transition from carpet to vinyl. It is a simple procedure that any professional installer can add to his or her arsenal. Start by placing a piece of tackless flush to the vinyl edge, and hammer the pins flat (Photo 1). Before you install the bar, run a bead of silicone caulk along the bottom edge of the metal. This will seal the doorway and help prevent water from the bath or kitchen from seeping under the bar and damaging the carpet or floor (Photo 2).
I seem to be a glue magnet, with about as much ending up on my hands and pants (Photo 4) as on the floor. One day while cleaning my hands, I found myself without paper towels and subsequently wiped the excess cleaner on my pants. To my great surprise, after my pants were washed the glue in the areas where I had wiped my hands was gone (Photo 5). I have since adopted the habit of carrying a tube of waterless hand cleaner in my tray or bringing a can of it to the job site.