During the 1920s, C.G. Conn developed a special type of saxophone pad specifically designed for use on saxophones with rolled toneholes called Conn "Res-o-Pads". These have an internal metal reinforcing ring which is hidden under the leather covering around the circumference of the pad. Their most notable feature is that the diameter of the pad extends over the rim of the key-cup, thereby giving a slightly wider surface area for the rolled tone-hole to seal onto. Rim impressions from Res-o-Pads are minimal.