Surplus SAE pattern aluminum sender level mounts.
Outer diameter 69mm, innner diameter 19.3mm. The inner diameter has a pipe ( taper ) thread but this can easily be turned out to suit your own purposes. The base is 4.3mm thick, the pipe thread section 10.4mm
There are also petrol proof seals that match this mount available as an option. The same SAE bolt pattern, 2.2mm thick. Outer diameter 69mm, inner diameter 29.4mm