It is the best grade of HSS steel. True engineering quality. These drill bits have been fully precision ground and heat treated for added strength and durability. Fully grounded bits are machined from a single rod and are better than regular rolled or drill bits. They are also more expensive to produce. They have long-lasting working ability and use an aggressive 135 degree parting point design. This set also comes with l carrying case, so you can stay organized in their correct and orderly positions. Starting from 1mm, these drill bits increase in size in 0.1mm increments135 Hss Split PointColor: SilverHoned High Speed Steel (HSS)General Use for Wood, Metal and PlasticsSizes from 1mm to 6mm in 0.1mm incrementsPackage Contents: 51 x Drill Bit Set1 x Box (Random Color, Can Not Be Colored)Only the above package content, other products are not included. Note: The light and different displays may cause the color of the item in the picture to be slightly different from the real thing. The allowed measurement error is +/- 1-3cm.