ABC Design holder - double

Updated version of the https://www.thingiverse.com/thing:4846587 from Dodu0815.

Improvements:
- triple mount instead of only two
- 2mm bigger distance between the three pins for better clearance between the mounted parts
- 0.5mm bigger gap between the groundplate and the "T-shaped" geometry for better mountability

Also available in this updated version as a double mount