British made Quality Reproduction Lucas Smiths Heater Control Knob
Long stem type also available along with many other similar parts

Lucas OEM reference 768378, CHR1

Fits Riley RM, Daimler 36 h.p. Limousine 1946-53 & DAIMLER 2t litre Models (except 'Consort') 1946-53 plus maybe other classic cars!
Approx dimensions: Width head 18.8mm, Height 13.7mm, post thickness tapers to 19mm 

Thanks for looking!