Screw size. Voltage stabilizer

I am still fighting with my non functioning fuel gauge on my 1973 Series 3. Replaced the sending unit and it worked for a day! Stopped working and tested the voltage from the stabilizer -5v using a peak reading meter. Replaced the stabilizer ( a pain to remove!) but in the process I lost the screw that fixes the stabilizer to the rear of the speedo. Any idea what size it is?

I temporarily grounded the stabilizer and now the gauges work (Fuel and temp) so that was the issue. I would like to fix the stabilizer where it is supposed to be though.

The gauge reads low (3/4 for a full tank). Not sure if that is a float issue or wiring.

I don't know about the screw, and the parts manual is no help, but, I would try BA sizes first.

For the low reading, a high resistance connection anywhere in the circuit could cause this. A poor connection between the tank sender and earth, a poor connection at the large multi-plug by the steering box, etc, etc