By 1920 Conn was producing a complete line of saxophones. In this area they had stiff competition from other big saxophone makers such as Buescher and Martin. Around 1917 Conn introduced drawn tone holes (after a patent by W.S. Haynes in 1914) eliminating the necessity of soft-soldering tone hole platforms onto the bodies of the instruments. Around 1920 Conn introduced rolled tone hole rims, a feature that enhanced the seal of the pads and extended pad life. Rolled tone holes remained a feature of Conn saxophones until 1947. By the late 1920s the success of Conn's latest "New Wonder" model saxophones with dance orchestras was gaining widespread attention, leading European manufacturers to produce horns closer to the deeper, richer, bolder "American" sound. Selmer (Paris) introduced the American-sounding "New Largebore" model in 1929 and the new Julius Keilwerth Company in Czechoslovakia produced saxophones influenced by the Conn design, including rolled tone holes and microtuners. As sax sales plateaued in 1928, Conn attempted to introduce a mezzo-soprano saxophone in the key of F and the "Conn-o-sax", a saxophone-English horn hybrid, but these instruments were soon discontinued after disappointing sales.