Handset with full range control knobs for servos 1 and 2, with a centre detent on both, two buttons for servo 3 and a single button for servo 4. The handset can be used for electric models too, with the ESC on S1. The Tx3.1 is ideal to replace the Roundhouse handset for their electrically powered models but will also work for their live steam models. An OMNI receiver will be required too. Use with STM-115 for boiler water indication - call for details.