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 hole under test, lock it in place, then remove it, measure with a micrometer or vernier caliper to determine the final hole size Quality: The dual-action handle is securely attached to the contact plunger and automatically self-centers. 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 that there is a good fit in the smallest hole the gauge will go into. Specification: Material : steel Drill sizes: 3/32inch, 1/8inch, 3/16inch, 1/4inch, 5/16inch, 3/8inch Screw extractors (6Pcs): 1(Dia: 4.0mm/0.15inch) for 3-6mm/0.15-0.23inch 2(Dia: 4.5mm/0.17inch) for 6-8mm/0.23-0.31inch 3 (Dia: 6.5mm/0.25inch for 8-11mm/0.31-0.43inch 4 (Dia: 7.5mm/0.29inch) for 11-14mm/0.43-0.55inch 5(Dia: 11.0mm/0.43inch) for 14-18mm/0.55-0.70inch 6 (Dia: 15.0mm/0.59inch for 18-25mm/0.70-0.98inch Storage Box Size: Approx. 19x10x4.5cm/7.48x3.93x1.77inch Packing list: 1 x 6 screw extractors 1 x 6 drill bits 1 x plastic storage box