The 1400 Small Wheel Attachment uses a 1/2" wide belt.  Wheels sizes from 5/16, 7/16 can be used with this attachment. 

The 1400 comes standard with the DA2212 wheel which is 7/16" x 3/8"

 

As with all 1400 series small wheel attachements you can also purchase different arms to run a wide variety of wheel widths and diameters.