Which screw for copper sundial

[slug68]

Which screw should you choose for a sundial in copper, does it have to be in copper?
The hole is 14 mm, hard to find that big, it will be attached to a pipe filled with concrete, maybe it would have been smart to cast in the bolt but that was not the case.

 

[andersmc]

Which screw should be used for a sundial made of copper, does it have to be copper? The hole is 14 mm, hard to find ones that large, it will be attached to a pipe filled with concrete, perhaps it would have been smart to cast in a bolt but that's not the case.

Stainless steel.

 

[Sharky58]

Expansion bolt and dome nut should be nice. I find M12 stainless dome nut at rostfriskruv.se. The largest dome nut in brass I find right now is M10. From what I understand, it's fine to mix stainless steel and copper.

/Göran