Replacement insert Bäst replaces the insert in valves of the type Bäst system. The best valve has been manufactured in about 50 different designs. The replacement insert is controlled with a thermostat or handwheel. NOTE - Non-limited thermostats. Common to all models of Best Valves is that there is an nut on an externally threaded valve body. Many also have a preset scale, embossed washer and handle to open and close the valve with. NOTE - For proper operation, existing valve housings are required to be in undamaged condition and the accompanying instructions are followed. The function cannot be guaranteed in case of aberrant valve design, incorrect installation, insufficient heat capacity or other conditions we cannot control.