I am trying to select the right helicoil to use in 6061-T651 Aluminium plate with 12.9 carbon Steel screw. The application will be indoors but humidity will not always be controlled so I was trying to keep the anodic index <0.25V.

The helicoil options are as follows:
0 = Stainless steel A 2, X 5 CrNi 18 10
1 = Bronze, CuSn 6
2 = Nimonic 90, NiCr 20 Co 18 Ti, silver plated*
3 = Stainless steel A 4, X 6 CrNiMoTi 17 12 2
4 = Inconel X 750, NiCr 15 Fe 7 TiAl, silver plated*
5 = Inconel X 750, NiCr 15 Fe 7 TiAl, bright
6 = Stainless steel A 2, X 5 CrNi 18 10, cadmium-plated
7 = Stainless steel A 2, X 5 CrNi 18 10, magazined**
8 = Bronze, CuSn 6, magazined**

I believe that I need option 6: Stainless steel A 2, X 5 CrNi 18 10, cadmium-plated as this will have an anodic index of -0.95, Aluminum 6061-t651 will have -0.9 and the steel fastener will have -0.85.

All the other materials seem to have galvanic indexes far away from Aluminium and therefore cadmium-plated seems to be the only option for my application.

I wanted to check that this is right and I am not missing anything as I haven't seen cadmium-plated called out for similar applications before.

Thank you for your help.