Fractional Tap, National Fine Thread, 3/4-In. x 163 4" x 16, national fine thread, fractional tap, carbon steel, ideal for routine maintenance, repair work & for rethreading where high accuracy & tolerance thread is not critical, straight flutes are ground to provide rapid chip removal for efficient threading, designed for hand threading work in a variety of materials taps produce a class 2b thread, use 11 16" drill bit.