Saddle Square - small - with clearance

Small saddle square.
Based on https://www.thingiverse.com/thing:1481552 .
Inspired by https://www.axminster.co.uk/veritas-saddle-square-ax480278 .

Main changes:
- smaller size
- riffled surfaces
- clearance in the corner

Designed in Onshape:
https://cad.onshape.com/documents/28978cc05b052631857bfc45/w/4e58623853085b13d8aa8fcd/e/fb9ef0fdc181a608c56a84c4