Round cup burs are made of the premium Vanadium steel for and accuracy This burr set includes 6 pieces, diameter of the burr are 2.1 mm Specific 3/32 inch ( 2.35 mm ) shank fits for electric rotary tool, drill, grinder, etc For carving of silver, jewelry, wood, walnut,olive core, beads, precious soft metal and more Colour:Silver Material:Metal Size:1.8mm Package Contents: 1 set x for engraving bits Only the above package content, other products are not included. Note: Light reflection 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.