Imperial (US Standard) Thread Gauge Imperial (US Standard Inch) thread gauge for standard 55 degree pitch threads. 20 blades.Size range 4 TPI through 48 TPI. Includes gauges for the following threads per inch (TPI) thread sizes: 4, 4.5, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 19, 20, 22, 24, 28, 40, 48