1 1/2″ (38 mm) O.D.
Cover snaps over mounting flange dimples to conceal screws.
Concealed mounting flange is 3 1/8″ (79 mm) O.D. diameter with two screw holes and three locking dimples adn is 1/8″ (3 mm) thick, type 304 thick stainless steel.
Cover is type 304 stainless steel with satin finish, 22 gauge, 3 3/16″ (81 mm) diameter.