Application: Used to get the precise hole and slot size, suitable for factories, schools, offices and other places High performance: Rigid handle and double-acting (self-centering) design allow for quick internal dimension checks. The spring tension is constant and the hand is even. Method of operation: extend the gauge into the tested hole, lock it in place, then remove it, measure with a micrometer or a foot to slide to determine final hole size Quality: The double-action handle is securely attached to the contact plunger and self-centers automatically. Constant spring tension provides even contact pressure. High quality, high rigidity, good wear resistance and durability. Precise grinding: The ends of both contacts are head treated steel and are precision ground to a certain radius so there is a good fit in the smallest hole the gauge will go into. Specification: Material: steel Drill sizes: 3/32, 1/8, 3/16, 1/4, 5/16, 3/8 Screw Extractors (6Pcs): #1(Dia: 4.0mm/0.15) for 3-6mm/0.15-0.23 #2(Dia: 4.5mm/0.17) for 6-8mm/0.23-0.31 #3 (Dia: 6.5mm/0.25) for 8-11mm/0.31-0.43 #4 (Dia: 7.5mm/0.29) for 11-14mm/0.43-0.55 #5(Dia: 11.0mm/0.43) for 14-18mm/0.55-0.70 #6 (Dia: 15.0mm/0.59) for 18-25mm/0.70-0.98 Storage box size: approx. 19x10x4.5cm Packing list: 1 x 6 screw extractors 1 x 6 drills 1 x storage box plastic