GG air control - for trim change just choose the 'CAP' if your 'CAP' pops off - otherwise you will need to obtain a complete air control and then just use the knob.
If you are just changing the trim - The top cap SNAPS off - to change trim you will need a new Cap and Trim for Cap - use the Trim Color drop-down menu for the metal trim
Complete Air Controls - if you want Brass, Chrome or Satin Nickel you will need to purchase the Trim for Cap - use the Trim Color drop-down menu
If your cap does NOT pop off then you have an older style and will need to purchase a complete air control and then any metal trim you may need