NPSpipe60° flankASME B1.20.1

2-1/2-8 NPS Thread Dimensions

2-1/2-8 NPS is a pipe National Pipe Straight thread. There are 8 threads per inch on a 2.8748 in major diameter, giving a metric-equivalent pitch of 3.175 mm. The size label is a nominal bore rather than a diameter.

Major Ø2.8748 in

Threads per inch8

Pitch (metric)3.175 mm

Pitch Ø2.7937 in

Tap drill2.75 in

Thread profile

millimetres unless stated

2-1/2-8 NPS — basic profile60° flank angle · Not to scale

Basic information

Designation: 2-1/2-8 NPS
Thread system: National Pipe Straight
Series: pipe
Standard: ASME B1.20.1
Basic profile: Unified profile, 0.8P thread height
Flank angle: 60°

Dimensions

Major diameter: 2.8748 in / 73.02 mm
Pitch (metric equivalent): 3.175 mm
Threads per inch: 8
Pitch diameter: 2.7937 in / 70.96 mm
Minor diameter (external): 2.6937 in / 68.42 mm
Minor diameter (internal): 2.7398 in / 69.59 mm
Thread depth: 0.1 in / 2.54 mm
Recommended tap drill: Ø 2.75 in / 69.85 mm

How these values are derived

tabulated standard values

This is a pipe thread, so the published dimensions are tabulated values from ASME B1.20.1 rather than figures derived from a formula: a pipe size is a nominal bore, and the relationship between that bore and the thread diameter is historical, not geometric. Diameters are quoted at the gauge plane; the thread itself is tapered, so the actual size changes along its length.

Compatible parts0 specification pages

No specification in this database uses 2-1/2-8 NPS. That is expected: the catalogue covers machine screws, bolts, nuts and washers, and pipe threads belong to fittings, which are a separate family of parts. The dimensions above are still the standard ones for the thread itself.

Neighbouring sizes in National Pipe Straight.

1-11.5 NPS 1-1/4-11.5 NPS 1-1/2-11.5 NPS 2-11.5 NPS 3-8 NPS