National Pipe Threads Tap Drill Chart

NPT and NPS threads share similarities in thread angle, shape and pitch (TPI – threads per inch). However, they differ in their design: NPT threads are tapered, while NPS threads are straight (parallel). Both types feature a 60° included angle. Tapered pipe threads are commonly used on pipe ends, nipples, and fittings such as couplings, elbows, and tees.

Outside of North America US pipe threads are not as common as British Standard Pipe (BSP) threads. 

Achieving a tight, leak-free joint relies on sharply angled threads. NPT seal is accomplished via metal-to-metal wedging. To ensure a proper seal, thread sealant or tape is typically necessary. On the other hand, Straight pipe threads require a gasket or O-ring to establish a seal. While NPT and NPS threads can engage with each other, they do not create a proper seal when used together.

NPTF threads, also known as Dryseal American National Standard Taper Pipe Thread, are specifically designed to achieve a more leak-free seal without relying on PTFE tape or other sealant compounds. These threads have a similar shape to regular NPT threads, but the crest and root heights are adjusted to create an interference fit, eliminating any spiral leakage path.

NPT & NPS Tap Drill Chart

Pipe Tap Size NPT & NPTF NPS & NPSF
Pitch (TPI) Drill Size (inch) Pitch (TPI) Drill Size (inch)
1/16 27 0.242 (C) – –
1/8 27 0.332 (Q) 27 0.348 (S)
1/4 18 7/16 18 29/64
3/8 18 9/16 18 19/32
1/2 14 45/64 14 47/64
3/4 14 29/32 14 15/16
1 11-1/2 1-9/64 11-1/2 1-3/16
1-1/4 11-1/2 1-31/64 11-1/2 1-33/64
1-1/2 11-1/2 1-23/32 11-1/2 1-3/4
2 11-1/2 2-7/32 11-1/2 2-7/32
2-1/2 8 2-5/8 8 2-21/32
3 8 3-1/4 8 3-9/32
3-1/2 8 3-3/4 8 3-25/32
4 8 4-1/4 8 4-9/32

The values displayed in this table are for direct tapping without reaming.

NPT – National Pipe Taper
NPTF – National Pipe Taper Fuel
NPS – National Pipe Straight
NPSF – National Pipe Straight Fuel

BSP tap drill chart

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