Current generation SRAM and Quarq power meters and cranksets use an 8-bolt mounting interface to secure the spider onto to drive-side crank arm. The 8 torx T20 bolts are pictured below:
All SRAM and Quarq power meters come with these bolts. In addition, the Quarq DZero DUB Crank Arms and the SRAM XX1 Eagle DUB Crank Arms also include them. Please note SRAM Force D1 Crank Arms and SRAM Red D1 Crank Arms do not include them.