Your BAR belt must have been made for tropical service - my guess ? odd there is no date or other markings.
Here is a photo of a WW1 BAR belt with the steel pocket to support the Model 1918 BAR butt stock, for firing the weapon while advancing. It did not work out. After the war and before WW2 most were converted by having another magazine pocket replace the steel support. These conversions are rare to find now.