This is the very best grade of HSS steel. True engineering quality. This set of drill pieces have been fully precision ground and heat treated for extra strength and durability. Fully ground bits are machined from a single bar and are far better that a normal rolled or twisted drill bit. They are also far more expensive to manufacture. These have a long lasting working capacity and use an aggressive 135 Degree Split Point Design. This set also comes with handy bespoke l carry case so you can keep them organised in their correct and tidy positions. Starting at 1mm these drills increase in size in 0.1mm increments Hss 135 Deg Split Point Color: Silver Ground high speed steel (HSS) General use for wood, metal and plastics Sizes from 1mm to 6mm in 0.1mm increments Package Contents: 51 x drill bit set 1 x Box (Color Random, can not choose color) Only the above package content, other products are not included. Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.