This is a sandingblock for 125mm sanding disks. You can use it in 2 ways:
1) use spray glue to make the block self-adhesive and use normal sand paper on it
or
2) use self-adhesive velcro fastener tape, which makes it possible to stick and remove the disks as on your sander.
I printed the model in PETG, 0.25mm nozzle, 20% gyroid infill (but i am sure other infill patterns and nozzle sizes also work, this is just my preference). Don'T forget to roughen the surface before applying glue.
The author marked this model as their own original creation.