These are stands and spacers for 3/4" pipe clamps. There are two versions of the stands, one short and one tall. The spacers can be used to keep the work flat and away from the pipe to avoid staining. These are great for panel glue-ups! I use spacers at the ends and under each of the glue joints.
This design was inspired by this accessory from Rockler:
https://www.rockler.com/bench-block-pipe-clamp-stabilizers
The author marked this model as their own original creation.