The Starrett Ball Attachment are hardened and measures .200" in diameter. It moves freely in the retainer, insuring positive contact with the anvil and spindle. The micrometer attachment is easily applied by snapping on to end of either anvil or spindle, thus permitting two attachments to be used together. Committed in providing customers with consistent and reliable solutions, Starrett has set the standard for precision, quality and innovation. Our products are long-lasting, robust with excellent service and performance. Starrett tools are designed to be user-friendly. Whether you're an experienced professional or an amateur when it comes to home improvement, our tools are handy and accessible. Starrett has set the standard for precision, quality, and innovation. Our products are long-lasting and robust with excellent service and performance. Manufacturing long-lasting and easy to use tools that provide consistent and reliable performance since 1880, Starrett tools are made with the highest standard of quality and workmanship, manufacturing more than 5,000 various tools, gages, and instruments, providing fine precision tools for industrial, professional, and consumer markets worldwide.