The correct bleed block sets your caliper pistons at the perfect starting point, which ensures the correct amount of fluid is in your brake system.
If the brakes are bled without a bleed block, you may unintentionally over-fill the system, which can lead to decreased power and/or the pads consistently rubbing the rotor.
Bleed blocks are included in the SRAM bleed kits (#00.5318.045.000) and (#00.5318.045.002)
You can find a list of Bleed Blocks and Pad Spacers for your specific model in our Brake Bleed Manual.