Railway Carriage Heater Switch Vintage Aluminium GWR Heater Knob Measures 12cm diameter on the face plate; which is 4mm thick. The switch mechanism at the back is 3.8m. The front Knob/Switch raises to around 3.2cm from the plate I have a few that have been stored in Paignton, Devon and came from a Railway Worker. Three listed with red detail an three listed with black detail This is the only one with this detail