Premier Double Z4 - PewterThe smart door threshold that joins carpet tiles and sisal Choose from 10 stunning metal finishes The Premier Double Z4 door thresholds are an elegant and secure means to join stick down carpets (such as Flotex), carpet tiles, flatweaves and sisal, in a doorway or across a room. Also suited to joining carpet titles or sisal to a hard floor (up to 4mm thick) by removing one base section (see fitting tips below). The two floors should be level with each