Hi Fabio,

The Smiths Fuel Gauge is listed for Vampire Mks 3 & 5 and Sea Vampire Mks 20 & 21 as 1352FG in AP1086, the M suffix being for Metric Calibration, the RAF Sec/Ref for 1352FG being 6A/2588 (Imperial Calibration)

Ref AP1086 Sec 6A to AL/18 and Smiths Aviation Instruments and Equipment Catalogue approx 1950

Hope that helps
Regards
Dave