Themain physical differences between NPT and NPTF are the flatness of the peaks and valleys of the threads. For the sake of our NPT tap drill chart, you simply need to know the distinction between an NPT fitting and NPTF. For example, reading across you’ll find that a 1/8 NPT tap will require an “R” size tap drill. A 3/8 NPT tap will BSW Insert Size: Drill Size: Wire Thread Insert Length: 1D: 1.5D: 2D: 2.5D: 3D: 1/8-40 : 3.3 mm : 0.125 : 0.188 : 0.250 : 0.313 : 0.375 : 3/16-24 : 5.0 mm : 0.188 A3/8 NPT thread calls for a 37/64 drill bit. How much of a problem am I going to have if I use a 3/4" drill bit? is that 1/64 going to cause me a ton of headaches? I am dong one hole this size. 93 Ranger on 37"s. Save Share. Reply Quote. Sort by Oldest first Thetap drill size for a 3/8 18 NPT thread is 0.482 inches and the tap size is 0.338 inches. It is important to use the correct tap drill size and tap size in order to ensure that the thread is properly formed and that the lineunder the tap drill diameter will show the thread tap size & thread series and form. If a controlled minimum tap depth or tight joint min. length is to be shown, the depth of minimum For hydraulic fittings, use 1/8 NPTF tap drill – Ø .339 For grease fittings with .125-27 NPTF thread, tap .125-27 NPSF to .31 for minimum full depth M39x 3.0. Tap Drill Chart (Standard 2B) Cut Tap Drill. Roll Tap Drill. Minor Ø. Major Ø. Tap Size. Cut Tap Drill. 3/64. ShoulderScrew Socket Head Socket Head Shoulder Screws size chart per. ASME B18.3 ; Spark Plug Threads Sizes and Tapped Hole Table; Tap Drill Hole Size based on Precentage of Full Thread Equation and Calculator; Dimension and Tolerances Table for T-Slots, Bolts, and Nuts T-Slots, Bolts, and Nuts per. American National Standard T-Slots InternalThread Size: 3/8-18 NPT. Length: 0.407". Material: 18-8 (304) Stainless Steel. Type: Free Running. Tap Size: 3/8-18 NPT STI. Drill Size: 21/32" (not included in kit, sold separately) Quickly and easily repair stripped or damaged threads, or create stronger original threads in die castings or plastics with our Helical Screw Thread Inserts. taperpipe sizes - npt: tap size: drill size: 1/8-27: r: 1/4-18: 7/16: 3/8-18: DrillSize* (inch) 0.242 (C) 0.332 (Q) 7/16 9/16 45/64 29/32 1-9/64 1-31/64 1-23/32 2-7/32 2-5/8 3-1/4 3-3/4 4-1/4. OyEZ.