You are purchasing one Antique 3Vees canary cage grit cup Boldly glazed lusterware in a golden yellow, from the 20's and 30's.
It is about 2 inches long - 3/4 inches wide and 1/2 half inch deep.   This vintage grit cup is a perfect piece of original cage furniture to dress up that Hendryx antique birdcage. This grit cup fits most early Budgie and Canary cages.

The American Radio Warblers, billed as canary songsters, were featured on live radio broadcasts during this era. The birds sang along with background music, and some of the recordings still exist on 78-RPM records.  
3 Vees, a seed, grit and egg food company, manufactured a small cage for the Radio Warblers, and it is highly collectible today. The yellow grit cup (like the one shown here) snapped between the bars of the small cage near the perch.