Product instruction: 2-0.7 (0.2mm-0.7mm) means: Diameter of motor shaft is 2 mm. Fit max 0.7mm drill bit. Also fit 0.2 mm to 0.7 mm drill bit.Concentricity adjustment method: Before lock bit need to adjust the concentricity,otherwise there will be a violent vibration,power on rotate awhile on the smooth surface of the floor or glass, lock bit after bit concentric. Specifications: Material: Brass Size: 25mm(L) x 8mm(Dia.) Diameter of backshaft (match the motor shaft): 2mm/2.3mm/3.17mm Shaft-Max Drill Bit Size(min-max): 2-0.7 (0.2mm-0.7mm), 2-1.2 (0.7mm-1.2mm), 2-1.5 (1.0mm-1.5mm), 2-2.5 (1.8mm-2.5mm), 2-3.17 (2.5mm-3.2mm), 2.3-0.7 (0.2mm-0.7mm), 2.3-1.2 (0.7mm-1.2mm), 2.3-1.5 (1.0mm-1.5mm), 2.3-2.3 (1.6mm-2.3mm), 2.3-3.17 (2.5mm-3.2mm), 3.17-0.7 (0.2mm-0.7mm), 3.17-1.2 (0.7mm-1.2mm), 3.17-1.5 (1.0mm-1.5mm), 3.17-2.0 (1.4mm-2.0mm), 3.17-2.5 (2.0mm-2.5mm), 3.17-3.17 (2.5mm-3.2mm) Item Included: 1pcs drill bits chuck( come with 2 screw