This three part sanding block  made to be very easy to put together.

Scale as you like, but be wary when scaling down, the bolt may need more clearance.

At 100% scale you needs 25mm wide sandpaper. The hexagonal pattern uses less material with same stiffness.

Recommended settings (best to use PETG)

Main block: 15% infill or more, 0.2mm layer, no supports needed

Bolt: use 15% infill, ideally PETG, 4 wall lines, 0.10mm layer.

Wedge: 15% infill or more, 0.2mm layer, no supports needed

None of the parts require supports.