Balanced to 25,000 RPM at G2.5. 0.0001 or better from taper to collet pocket. Taper ground to AT3 accuracy or better. Each holder lab certified for accuracy and balance.CAT 50, ER 16 Collet Chucks. CAT 50 x ER 16 - 4.00, hex nut. Other Available CAT 50 ER 16 Collet Chucks. Listings are described with detail information.