White Victorian Register 6" x 12" for a 4" x 10" Opening

Description

This is new, never used; I've had it for at least 10 years but didn't use it in my project.    It might be from Signature Hardware but from many years ago (they don't have it now).
Duct opening would be 4" x 10" and outside edge is 6" x 12".    Screws come with as shown.   Works perfectly.    Flanges adjust.
This looks like cast iron but it can't be because it's too light-weight.    Must be aluminum.     It would be perfect in a ceiling.
Message with questions.