VERY UNUSUAL DOUBLE-ENDED WRENCH WITH RULE MEASUREMENTS

First of these I've seen. Measures 10.5" total length. Wrench sizes are 1 1/8" and 11/16". The large end was for wheel nuts. The gas tank was under a hood above the engine. In the centre of the tank was the filler cap. The small end of the wrench would fit vertically through the filler cap hole to measure how much fuel remained in the tank. Embossed 'M 4' on the backside. Ford or Ferguson tractor.