A slug tuned coil from a straw and a brazing rod.

I drilled a bolt down the center and tapped it to accept the tuning slug. This allowed me to use a nut to fasten it to the faceplate. You could just use a nut glued to the straw and faceplate for a permanent installation.
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An iron core could be used but for RF the brass has less loss and gives an increase in frequency as you screw it in.

EDIT:
This post explains the effect of the brass slug

.spacing-coil-from-chassis-or-shield

 EDIT2:
This one is same concept with a different support and pictures of the construction.

Adjustable coil