Metal Corset D-Ring in Antique Brass, Nickel, or Black Nickel. I love to use these on my Callisto and Paradigm Crossbody bags! They are perfect for wallets or clutches as well, they're nice and subtle and the d-ring can flip out of the way when not in use. 
 
D-Ring plus rivet area measures .75" wide in total. D-Ring itself is 1/2"
 
Sold in sets of 10 (rivets no longer included on new sets)