Thenominal size of a Pipe Tap is that of the pipe fitting to be tapped, not the actual size of the tap. The thread tapers 3/4 of an in. per foot. All Pipe Taps furnished with a 2-1/2 in. to 3-1/2 in. thread chamfer. NPT threads require the use Whatis the nominal knockout diameter for 1/2 inch trade size Conduit? The nominal knockout diameter for 1/2 inch conduit is 0.875 inches. 21/2 2-5/8 2-39/64 2-21/32 3 3-1/4 3-15/64 TAP DRILL SIZES METRIC TAP DRILL SIZES Cutting Taps based on approx. 75% thread Forming Taps based on approx. 65% thread Cutting Taps based on approx. 75% thread Forming Taps based on approx. 65% thread TAP SIZE CUTTING TAP DRILL SIZE FORMING TAP DRILL SIZE TAP SIZE TapDrill Sizes for M16. If not specified, assume a thread depth of 75%. You can learn more about thread depth in tapping here. To get the tap drill size in other depths, use our Tap Drill Size Calculator . Thread Depth. Tap Drill Size (Inch) Tap Drill Size (mm) 55%. 0.574. Includessize of: 1/8" - 27 npt, 1/4" - 18 npt, 3/8" - 18 npt, 1/2" - 14 npt, 3/4" - 14 npt Versatile set suitable for both personal and professional use. Clean and Re-Thread Damaged or Jam Pipe Threads with Ease - Ideal for Pipe Fittings, DIYers, handymen, and professionals who need to repair damaged pipe threads. Bad4URHeart 798 posts · Joined 2002. #7 · Jan 3, 2006. The correct bit for any tap should be 90% of the tap size. NPT requires an 50% increase adjustment since it is measured differently than drill bits. Therefore, 1/2 * 1.5 (50% increase) = 0.75. 0.75 * 90% (tap to drill bit conversion factor) = 0.675. Drill bit sizes in that range. nominalper of of overall taper regular taper regular drill size inch flutes threads length regular (dryseal) regular (dryseal) sizes npt nptf nptt nptft 1/16 27 4 11/16 2-1/8 18.66 18.66 33.26 33.26 “c” interrrupted and straight thread 1/16" to 2" NationalPipe Thread is an American standard defined in ASME B1-20.1 The most popular series is Tapered Pipe Thread (NPT). However, other series, such as NPTSC and 1qI2Q7o.