Remix of https://www.printables.com/model/30496-very-printable-strap-adjuster by @Zenfunk, with ideas from @gloda:

1. Added slot so it can be attached to closed strap loops (without re-stitching).
2. Added fuzzy skin to the bar making contact with the moving strap to reduce slipping.

25mm model.  Let me know if another width is needed.