In the case of coils, adjacent aluminum will reduce value, and adjacent steel will increase value. Since brass conducts and is nonferrous, I would wager it would also reduce value, though minimally.
This is one of the reasons that titanium is used as a voice coil former. There are no eddy currents in titanium since it is a poor conductor. Aluminum formers are normally not a complete ring for this reason to not allow the eddy currents to flow.
In the case of the coils in the amplifier CLC up a few posts, I would likely use an acrylic/nylon mount and a nylon bolt. Some nylons don't melt until over 400 degrees, and I don't believe amplifier supplies should ever get that warm. I would also likely dip the coils in polyurethane before mounting to prevent any contact to windings. In Foil coils, there is a film layer between each winding, and either an edge of film that is a couple mm wide beyond the copper, or an actual bonded-resin surface on the flat faces. I know some Alphacore/Goertz and Erse FoilQ products have that bonded rock-hard resin surface. I will also say that some loudspeaker xover coils advocate against using them as PSU chokes. Some are just not able to be used in this manner without some form of breakdown due to current capacity or construction methods.
In the case of mounting the air-core, I would use a minimum of brass, and nylon or titanium bolts are likely preferable. You don't want any saturation products.
Later,
Wolf
This is one of the reasons that titanium is used as a voice coil former. There are no eddy currents in titanium since it is a poor conductor. Aluminum formers are normally not a complete ring for this reason to not allow the eddy currents to flow.
In the case of the coils in the amplifier CLC up a few posts, I would likely use an acrylic/nylon mount and a nylon bolt. Some nylons don't melt until over 400 degrees, and I don't believe amplifier supplies should ever get that warm. I would also likely dip the coils in polyurethane before mounting to prevent any contact to windings. In Foil coils, there is a film layer between each winding, and either an edge of film that is a couple mm wide beyond the copper, or an actual bonded-resin surface on the flat faces. I know some Alphacore/Goertz and Erse FoilQ products have that bonded rock-hard resin surface. I will also say that some loudspeaker xover coils advocate against using them as PSU chokes. Some are just not able to be used in this manner without some form of breakdown due to current capacity or construction methods.
In the case of mounting the air-core, I would use a minimum of brass, and nylon or titanium bolts are likely preferable. You don't want any saturation products.
Later,
Wolf
https://youtu.be/OzNvicZWZ_A 
That was very helpful, thank you, Wolf. I will look for Ti bolts. Hm, I will try with this inductor. It has a lower resistance than my other inductors. 2.7mH with 0.45 ohm, and should run cooler. I have isolated the two peices of foil with two layers of shrink tubing and the bottom of the coil is isolated with 2mm silicone pad designed for frying pans. I can try to raise it more from the bottom.
That was very helpful, thank you, Wolf. I will look for Ti bolts. Hm, I will try with this inductor. It has a lower resistance than my other inductors. 2.7mH with 0.45 ohm, and should run cooler. I have isolated the two peices of foil with two layers of shrink tubing and the bottom of the coil is isolated with 2mm silicone pad designed for frying pans. I can try to raise it more from the bottom.
If zip-ties would melt from heat, then you're in trouble because the insulation on those is also thin plastic. If the coil insulation is more robust than nylon (standard ziptie material) from a thermal standpoint, these could be an option: PEEK High Temp Cable Ties
Yes, but note the important difference: In toroidal transformers the coil is wound around the toroidal core, the magnetic flux is limited to the toroid, there is no net flux in the inner opening, stray fields neglected.
In the coils shown here, the ferrous bolt is in the center of the coil, that's where the maximum of the magnetic flux is. It will change the inductance of the coils as well as cause unpredictable effects when going into and out of saturation...
Regards,
Andreas
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