Fitment:  

ISO30 ER16 Collet Chuck 70mm G2.5 30000 RPM CNC Tool Holder

Description：

70mm (2.75 inch) length
.00016" or 4 micron precision
Balanced at G2.5 30,000 RPM standards (might be marked GM2.5)
ER16 collet size

Balancing helps with vibration which prevents premature bearing failures in the spindle.    Balancing was performed on a machine to meet the G2.5 specification for 30K rpm. 

Thanks for Looking!