The thickness of frames (Small or Large) is predetermined relative to the size of the print, so all you just have to choose is the colour and either a Standard or Deluxe specification.
Small frames are automatically adopted for small prints (these are the smallest 2 available sizes of any given print). Large frames are automatically adopted for all the other bigger sizes of print. So when deciding between Standard and Deluxe frames and their colours, please view the appropriate frame size for your print size!
For further information on frames and finished frame sizes click here.