15mm x 4mm
I originally created this mark for a written monogram back when I was in college. About ten years ago, I had a branding iron made for woodworking projects, and subsequently a marking stamp for jewelry. (BTW, I ordered my stamp through @RioGrande, and their prices were better than the others I've seen in the original topic.)
I use this for just about everything I make, bracelets, rings, pendants, and even tiny charms.