- H6 arbor tolerance to improve cutter chattering and overall cutting tool life - T.I.R. 0.0002" measured from BT30 taper to face and arbor - Made from alloy steel harden to 54-60 HRc - Taper ground to AT3 or better accuracy standard for maximum contact with spindle. All of SHARS CAT/BT/HSK tool holder use Stotz Air/Electronic Gaging for production and finish inspection. Stotz has been chosen by major aircraft companies as the best and most consistent gaging for tool holder shanks - All critical surface are precision ground - Each holder comes with a lab certificate on its taper accuracy and runout measurement