SRAM Red DZero and Quarq DZero HB (hidden bolt) power meters use a slightly different bolt pattern than your typical 5 bolt NHB (non-hidden bolt) design. The HB design is offered to better work with the SRAM Red, Force, and Rival chainrings that also use an HB design.
The Quarq DZero Carbon and the Quarq DZero Aluminum are offered in an HB or an NHB variant. The NHB variants are better suited for use with non-SRAM chainrings such as Praxis or WickWerks.
See below for examples of an HB power meter and an NHB power meter: