Pipe Thread Tap and Drill Size Chart ANSI

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Machinist Tap - Drill Chart for ANSI Size Threads
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The following is a ANSI Standard Pipe Thread Recommended Tap size and Drilled Pilot Hole for Taper

National Pipe Thread Taper ( NPT ) is a U.S. standard for tapered threads used on threaded pipes and fittings . In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal.

Threaded pipes can provide an effective seal for pipes transporting liquids , gases , steam , and hydraulic fluid. These threads are now used in materials other than steel and brass, including PTFE , nylon , bronze , and cast iron .

The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide the seal. As the thread body is tapered (0.75 in/ft or 62.5 mm/m) a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the crests and roots of the threads because of the taper). This means that NPT fittings should be burr-free and lubricated using a lubricating material like lubricating paste or tape . The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.

Commonly used sizes are 1/⁄ 8 , 1/4 , 3/⁄ 8 , 1/2 , 3/4 , 1, 1 1/⁄ 4 , 1 1/2 , and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than 1 ⁄ 8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes.

Related Resources:

National Standard Taper Pipe Threads Size NPT Chart

TAPER PIPE SIZES - NPT
TAP SIZE DRILL SIZE
1/8-27 R
1/4-18 7/16
3/8-18 37/64
1/2-14 23/32
3/4-14 59/64
1"-11-1/2 1-5/32
1-1/4-11-1/2 1-1/2
1-1/2-11-1/2 1-47/64
2"-11-1/2 2-7/32
2-1/2-8 2-5/8
3"-8 3-1/4
3-1/2-8 3-3/4
4"-8 4-1/4
STRAIGHT PIPE SIZES - NPS
TAP SIZE DRILL SIZE
1/8-27 S
1/4-18 29/64
3/8-18 19/32
1/2-14 47/64
3/4-14 15/16
1"-11-1/2 1-3/16
1-1/4-11-1/2 1-33/64
1-1/2-11-1/2 1-3/4
2"-11-1/2 2-7/32
2-1/2-8 2-21/32
3"-8 3-9/32
3-1/2-8 3-25/32
4"-8 4-9/32

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