The phrase "nail head" refers to the top part of a nail where it is struck with a hammer. It can also be used figuratively to mean hitting the main point or key issue.
Sentences with «nail head»
I'm also planning on making a head board with nail head trim and will be using your tutorial as a guide. (centsationalstyle.com)
We have a piano and a club room chair and couch with nail head trim. (lehmanlane.net)