Technical Model A Instrument Panel

I don't recall exactly, but would guess either 2 1/16 or 2 1/8.

 

Hi, I just got a 1928 Model A roadster pickup and I was hoping you could tell me what that star shaped socket at the top center is for, mine has that and I have no idea. Thanks

 

Gas gauge. If you look dead in the center of it it will have numbers 1/4, 1/2 etc.

 

This was a period accessory - rare and expensive today. I think there were repops sometime in the 60s.
Look at the Model A parts suppliers they have 1 and 2 gauge panels that fit under the stock dash. They all use 2" gauges. There are 1 1/2" gauges available that I think would look better in the small A interior.
This is the single mount - basically just a strap that holds the gauge and uses the bottom 2 dash screws. The SW wing gauges look period correct.

 

See parts for sale
https://www.jalopyjournal.com/forum/threads/1931-model-a-aristocrat-dash-panel.1327461/

 

The star shape is so you can put a square bar in there and unscrew it.