This is a 15mm dovetail mount for Fermunoz's barn-door astrophotography tracker. You can use this dovetail to mount a small, cheap red-dot sight or other finder scope for perfectly aligning the barn-door tracker with Polaris.
This is designed to fit Fermunoz's Barn_Door_Tracker2_v3 bearing mount.
Print vertically, with support for the alignment tabs.
Drill pilot holes and attach it with countersunk screws to ensure your dovetail scope will slide on without interference.