[RFI] Choke questions

[Andy KU7T]

Hi,
these may dumb questions (I am a choke newbee, but working myself up to the skillset to build my own to specific needs)...

A recommended method and material to use is #31 and a #12 THHN pair of wire (non-twisted). Since these are un-shielded wires, wouldn't this cause additional RF exposed where we do not need it?  Or does the field cancel because of the closeness of the pair of wires?

I would also have the opportunity to use thinner coax of the right impedance to make a choke. Why is the THHN wire better than coax?

Thanks and 73
Andy
KU7T