From the manufacturer

The Odyssey Milled Collection RSX V-Line Fang Putter is a hybrid mallet putter developed from Odyssey's never ending pursuit to innovate insert technology.

The Milled Collection RSX V-Line Fang Putter is milled from 1025 carbon steel for premium quality, feel and performance.  A precision milled sound chamber pocket is located behind the 17-4 stainless steel face to enhance feedback and feel.  The face has been chemically etched with Odyssey's patent Metal-X oval pattern which provides a better roll off the face.  A stabilizing crossbar is also used to enhance sound and feel across the face.