This is a 4-pack of PRO Gallerie Wrap: (20" Center Braces) from Hahnemuhle . They are designed for use with the PRO Gallerie Wrap fine-art framing system. Stretcher Bars in the PRO series are 1.75" deep and 20" or longer in length, meaning that the extra-large dimensions of these frames can sometimes require extra support. These center braces can be used to increase the strength and rigidity of your frame.