When it comes to optics, there are many different ways to measure them. In inches, 6.3 is the standard. This is because the U.S. customary units of measurement are inches (22.4 mm), quarter inch (1.27 mm), and millimeter (0.39 mm). The metric units of measurement are millimeters (0.39 mm), centimeters (1.57 cm), and meters (3.79 … Continue reading What Is 17mm In Inches – Accurate Answer