ER collet chucks are a great choice for milling, drilling, boring, and reaming. Runout is guaranteed to be less than 0.0001" TIR max between the O.D. taper and the I.D. socket. Overall system accuracy guaranteed to be 0.0003” TIR or better when using Royal Ultra-Precision ER collets. Tapers are ground to AT-3 specifications or better to ensure a precise, rigid fit with the machine tool spindle taper. The clamping nuts are ground to ensure near-perfect roundness. This helps ensure maximum accuracy, minimizes vibration, and provides outstanding holding power. All Royal ER collet chucks are balanced to G2.5@18,000 rpm for high-speed operation. A serialized balance certificate is included with each tool.