That particular extension looks like it may be steel.
Not meaning to pick a fight here ---
Ford did also make this extension in Aluminum and it was quite beefy/strong. I had one on my FFR Spec Racer Cobra for 3 years and I would bet it is still on that car since I sold it 10 years ago... I will confess that I did not have an electrical gauge sending unit on it though. Rather a 3/8 (believe) NPT to AN3 adapter and from there a braided line to the guage.