0-30 3/4 Pressure Gauge with adapter to fit 1/4 BSF thread on Mamod models .Use in place of whistle. Do NOT  use in place of safety valve ! When useing this it is VERY importnt not to overfill the boiler beyond the mark indicated on the sightglass. Doing so will result in water being forced up into the pressure gauge causing permenant damage. This invalidates any warranty given. .