This very nice looking gauge is a WW2 Weston Indicator MK IB Aircraft Oil Thermometer 6A/1342. An Air Ministry Meter dating to 1943.
The instrument is in fair used condition with rusting on the rear and some loss of paint on the face and rear. However, it won't zero and it has lost its pointer. The price has been adjusted accordingly.
Approximate size (WHD): 6.5cm x 6.5cm x 5.7cm
Face Diameter: approx. 4.7cm
This type of instrument was used to measure the engine temperature in aircraft of the RAF, RCAF, and RAAF including the Spitfire, Mosquito and Lancaster. This one is unusual in that the face is yellow for improved luminosity.
Although it is not marked with a maker's name, it was probably made by the well respected aircraft instrument maker, Sangamo Weston, Enfield, Middlesex: I've attached an image of a 1945 advert for a Mark II Weston aircraft gauge.
Summary
Made by Sangamo Weston Ltd, Enfield, Middlesex, England. MKIB
24 Volt Aircraft Oil Temperature Gauge measures 0-120 ºC
