For interior stained glass windows frames we recommend the 100 Series or the 200X series. 

The 100 Series is designed with the smallest sight lines making it the best choice for smaller interior stained glass windows. The 3/8″ glazing rebate provides the most exposure for the stained glass while 1/8″ thick walls makes it strong enough for most applications.

The 200X Series is stronger and is used for larger windows.  It has a 5/8″ glazing rebate for larger glass openings.