Big Gator Tools BGRSTIUNC100SNP 6-32-9/16 V-Tap Guide/STI (Standard UNF Size) Universal & Portable Screw Thread Insert (STI) V-Tap guide provides perpendicular alignment of STI ground thread taps used for Heli Coil inserts on flat, round or square cornered materials 9 guide holes cover 10 Unified Course Thread (UNC) ground thread STI tap sizes: 6-32, 8-32, 10-24, 12-24, 1/4-20, 5/16-18, 3/8-16, 7/16-14, 1/2-13, 9/16-12 Heat treated nickel alloy steel provides durability and accuracy Precision ground base provides perpendicular alignment of STI tap on flat materials