Change default size of thumbnails in Preview sidebar

There is no user preference or command-line setting to set the Preview thumbnail size. When you pass your pointer over the boundary between the document and the thumbnail gallery, it will trigger a resize pointer, and you can collapse the thumbnail gallery (and implicitly the thumbnail size) as far as it will go to the left.

Preview remembers this minimalized thumbnail gallery width between application invocations, and that will inherently result in the smallest setting for the thumbnails.

Werschulz wrote:

I would like to change the default size of thumbnails in the Preview sidebar (for the record, I prefer more thumbnails at a smaller size). Is there some way to do this?

You can submit your Apple Feedback for features you would like to see: http://www.apple.com/feedback