Bergeon 6740 gauge is made of metal making it sturdy and durable. It allows you to easily measure the diameter, tube opening, stem thread, lug width, and tap sizes of your watch crowns. With this one stop shop tool, repairing or replacing a watch crown is a breeze. Measures watch crown diameter (mm) Measures watch crown tube opening (mm) Bergeon 6740 gauge is made of metal making it sturdy and durable. It allows you to easily measure the diameter, tube opening, stem thread, lug width, and tap sizes of your watch crowns. With this one stop shop tool, repairing or replacing a watch crown is a breeze. Measures watch crown diameter (mm) Measures watch crown tube opening (mm) Measures watch crown stem thread (mm) Measures watch crown lug width (mm) Measures watch crown tap sizes (mm) Size 4 X 3 X 1" Inches (118 X 85 X 2mm)