The choice between a flat micrometer anvil and a spherical micrometer anvil really comes down to a matter of measurement type. Spherical anvils are used to collect measurements when working with a curved or cylindrical surface. When a single tangential point of contact is needed for a measurement, then a spherical anvil is also ideal. One disadvantage of using a spherical anvil is needing to account for the diameter of the ball in your final measurement. Flat micrometer anvils, alternately, are used to measure when a flat surface is involved. These are the most commonly purchased and owned types of anvils because of their broad application. Importantly, flat anvils require regular flatness checks to maintain accuracy. If you are intending to be working with rounded surfaces like balls or wall thickness on a tube, then a spherical micrometer anvil is likely best. However, if you are typically going to be measuring flat surfaces and structures, then a flat micrometer anvil is what you will need.