IEif a person Drills with a Q Drill (.332") and Taps 1/8-27 to a depth of .3925" it is going to be a different Minor Diameter than if you use an R Drill (.339") and Tap it the exact same depth. Whereas if we refer to the paper weight on my desk (machinery's handbook) then we find that the Basic Minor is .3339". Hereare some tips on tapping clean, leak-free threads: Use the right drill size – To accommodate the taper, the hole must be slightly larger than the thread‘s major diameter. Follow tap drill charts carefully. For a 1/4" NPT thread, this will result in 4-6 fully engaged threads after hand-tightening. Generally 3-5 engaged threads is Whilestandard screw threads generally use between 10 and 12.5 percent truncation, the pipe threads seem to use a smaller percentage. The 1/16 - 27 NPT in particular uses between 0.0012" (minimum) and 0.0036" (maximum) truncation at both areas. That translates to percentages between 3.74% and 11.2%. I have found that using a 2031. 2-1/16. 2.062. 3-1/8. 2.180. 1. Countersink. It is considered good practice to countersink or break the edges of holes that are smaller than F (max.) in parts having a hardness which approaches, equals, or exceeds the screw hardness. If such holes are not countersunk, the heads of screws may not seat properly or the sharp edges on holes 14" Carbon Steel NPT Tap and 7/16" HSS Drill Bit in plastic pouch. NPT Tap and Drill Set comes in an easy to maintain plastic pouch; Set contains one Carbon Steel NPT Pipe Tap and the matching size Black Oxide High Speed Steel Drill Bit; Carbon steel NPT pipe taps are designed to clean and or re-thread damaged or jammed pipe threads Fora standard tap, you will need a 7/16-inch drill bit, and for a bottoming tap, you will need a 1/4-inch drill bit. The tap drill diameter for a 1/8-27 NPT pipe thread is 0.265 inches. To determine the tap drill size, all you need to do is subtract the thread pitch (TP) from the outside diameter (OD). Hopefully, this blog post has been MIBRO1/4" 18 NPT Pipe Tap - Titanium Coated. 0 Reviews. Item: #1142-622. Product Overview Description. For cutting internal threads; Standard, pipe and metric sizes; Produced to exacting specifications; Tough, carbon tool steel for long life; Resist rust and tarnish; Cut cleaner, more accurate threads; 1/4-18NPT; Use drill size: 7/16 BSPPG 3/4 : Brith Pipe (BSP) Thread Dimensions and Tolerances. All the relevant data for this tread in one spot. BSPP G 3/4 : Brith Pipe (BSP) Thread Dimensions and Tolerances. Tap Drill Sizes Charts; GLOSSARY; LEARNING Menu Toggle. How to Use the Machining Doctor; Dryseal Pipe Threads (NPTF) British Pipe Threads (BSP) gF0B.