The small Simpson Case travel container is made specifically for the Simpson Case brush. It will work with other similarly sized brushes (e.g. Simpson Classic 1, Simpson Duke 1, Omega 11047).
Size: Inner diameter 33 mm, height 86 mm
The large Simpson Case travel container is quite larger than the small and can hold an assortment of brushes.
Size: Inner diameter 43 mm, height 124 mm