Pnp rba coil

Hello, i use Voopoo Drag x mod with with factory coils and i want to buy the rebuild-able coil by voopoo in order to start making my own coils but i i am so confused. Do i need to buy the rba coil just once and then just replace the wire and the cotton when it is needed or i replace the head coil every time i replace the wire? Thank you.

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