1.R8 collet material:65Mn 2.Hardness:clamping part HRC55-60 3.round,square,hex hole 1.Made of special elastic steel material ... 3.USed for boring,milling,drilling,etc Antirust surface of collets:Feature:1.Antirust 2.Improve the hardness and endurance of ... ,Accuracy stable 4.Surface more smooth ,Feel comfortable,Appearance nice R8 collet