3.8mm and 4.0mm thick SRAM Maven brake caliper block to aid in the piston massage process.
Details of the piston massage process can be found on the SRAM Mineral Oil MTB Disc Brake Installation, Hose Shortening, and Bleed Manual ("Disc Brake Piston Massage" section).
PLA worked fine for me (100% infill), I suspect PLA+ or PETG would be more ideal.
The author marked this model as their own original creation.