So no matter how beautiful your cover is full size, you have to have a beautiful thumb nail as well. (theselfpublishingtoolkit.com)
Your treats should be about the size of a regular thumb nail. (dog-care-centre.com)
This will aggravate the readers, but this is my personal thumb nail for judging global warming and cooling during this 10,000 year break between Ice ages. (wattsupwiththat.com)