Application: Used to obtain the accurate size of the hole and slot, suitable for factories, schools, offices and other places High performance: The rigid handle and double-acting design (self-centering) allow for quick checking of internal dimensions. The spring tension is constant and the hand is uniform. Operation method: 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 double-action handle is securely fixed on the contact plunger and automatically self-centers. The constant spring tension provides uniform contact pressure. High quality, high rigidity, good wear resistance and durability. Precise Grinding: The ends of the two contacts are made of head-treated steel and are precisely ground to a certain radius so that there is a good in the smallest hole that the gauge will enter. Specification: Material: Steel Drill Bit 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/7.48x3.93x1.77" Packing List: 1 x 6 Screw Extractors 1 x 6 Drills 1 x Plastic Storage Box