Choosefrom our selection of 1/4"-28 adapters in a wide range of styles and sizes. AC Adapter Power Supplies AC Adapter Power Units Adapt-a-Drive Drill Chucks Adapter Cords Adapter Nuts Adapter Plates Adapters For Easy-Adjust High-Pressure Switches Bearing Adapter Sleeves BNC Adapter Tees DIN Panel Adapter Thread Size. 1-6 4. 2-5 6. 3-5 Todetermine the proper drill size for 75% thread on a special pitch tap use the following formula: [Major Diameter of tap, in inches] - (.975 divided by the number of Threads Per Inch) = Drill Size [in 1000ths of an inch.] EXAMPLE: To find the drill size for a 1/4-32 tap: TapDrill Size. The most important factor to consider when drilling a hole for a 1/4-inch tap is the tap drill size. This refers to the size of the hole that needs to be drilled to ensure that the threads of the tap fit properly and the threading is secure. The tap drill size for a 1/4 inch tap is typically #7, which is 0.201 inches in diameter. NPTThreads Dimensions. NPT THREAD SIZE & PITCH DASH SIZE MALE THREAD MINOR OD FEMALE THREAD ID; inch – TPI: mm: inch: mm: inch: 1/8 – 27-02: 9,9: 0.39: 8,4: 0.33: 1/4 – 18-04: 13,2: 0.52 Subtract approximately 1/4”(6 mm) from thread measurement for nominal pipe size. Pitch is Threads Per Inch (TPI). Read More. RYCO NPSFAmerican Pipe Thread ANSI B 1.20.1, American Thread, Pipe, Fitting. NPSF American Pipe Thread NPT Thread (USA) NPTF Thread (USA) NPSC Thread (USA) NPSF Thread (USA) Drill Size mm: TPI: Pitch mm: 1/16" - 27 NPSF: 7.582: 6.304: 27: 0.940: 1/8" - 27 NPSF: 9.929: 8.651: 27: 0.940: 1/4" - 18 NPSF: 13.236: Fullsize is when you take a branch of the same size as run pipe size, for example, 3 inches to 3 inches. And reducing size is when branch size is less than run pipe size. For example, 3 inches to 1 inch. Threadolet ’s end is suited for the threaded connection. This olet is available in class 3000 and class 6000 pressure-temperature ratings. Findingthe Diameter: Look for the fraction marking near the shank of the bit. It’s typically stamped above the thread. Measuring Diameter: If you can’t find the stamped 14 inch tapby: Buster. I agree with you Bill, haha. He may have meant what drill bit size he needs to tap a 1/4 inch NPT thread, which would be 7/16″. 1/4 inch pipe quick connects can have different sizes of connections for different sizes of pipes, from 1/8″ pipe up to 3/4″ pipe thread with the most common being 1/4″ NPT. Choosefrom our selection of pipe thread repair inserts in a wide range of styles and sizes. In stock and ready to ship. Drill Bit Size: For Max. Hole Dia. Pkg. Qty. 1/4. 0.394" 33/64 " 33/64 " 12: Drill Bit, Through-Hole Tap, Installation Stainlesssteel. K. Grey cast iron, malleable and spheroidal iron. N. Aluminium and other non-ferrous metal. S. Special, super and titanium alloys. H. Hardened steel and chilled cast iron. R7l0.