1、Drill bit is made from carbon steel and countersink is made from good quality 45# steel which ensures a long service life 2、Combined drill bit and countersink bit is great for drilling, chamfering, deburring and countersinking 3、There are 10 sizes of 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 10mm and you can choose the one you need 4、Five flutes design provides small chip loads and quicker removal, it can discharge wood sawdust more rapidly and smoothly 5、Suitable for drilling holes on board of low hardness such as wood, plastic and other soft material Features: Drill bit is made from carbon steel and countersink is made from good quality 45# steel which ensures a long service life. Combined drill bit and countersink bit is great for drilling, chamfering, deburring and countersinking. There are 10 sizes of 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 10mm and you can choose the one you need. Five flutes design provides small chip loads and quicker removal, it can discharge wood sawdust more rapidly and smoothly. Suitable for drilling holes on board of low hardness such as wood, plastic and other soft material. Specifications: Material: Carbon steel(drill bit), 45# steel(countersink) Countersink Flute: 5 Drill Bit Diameter: 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 7mm, 8mm, 10mm, 3-10mm(3/4/5/6/7/8/10mm), 3-6mm(3/4/5/6mm)(Optional) Countersink Diameter: 15.8mm Hex Key Size: 55 x 20mm Quantity: Your choice Package Includes: 1pc(or 1 set) x Countersink Drill Bit 1 x Hex Key Note: There are only 7pcs in 3-10set, and only 4pcs in 3-6set.