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Description
Taper reamer 1:16 — 3/4" for NPT pipe threads
Technical specifications · ASME B94.2-1995 standard
TypeTapered 1:16hand reamer
For thread3/4" NPT3/4 inch · NPTF · Rc
StandardASME B94.2ASME B94.2-1995
MaterialHSShigh-speed steel (HSS) (M2)
| TECHNICAL DATA | |
|---|---|
| Reamer | 3/4" NPT (included angle 3.58°) |
| Tip diameter d1 | 22.25 mm |
| Larger diameter d2 | 24.40 mm |
| Shank diameter d3 | 23.0 mm |
| Overall length | 82 mm |
| Flute length | 35 mm |
| Square drive | 17.5 mm |
| Intended use | 3/4" NPT · NPTF · Rc thread |
| Material | HSS — high-speed steel (grade M2) |
| Standard | ASME B94.2-1995 |
What a 1:16 taper reamer is used for
Preparing a hole for a taper pipe thread
The 1:16 taper reamer in size 3/4" is a hand-operated finishing tool that gives a drilled hole a precise 1:16 taper ratio — the same as the American taper pipe thread NPT (National Pipe Taper). The tool is made from high-speed steel (HSS) HSS (grade M2) according to the standard ASME B94.2-1995, and its tapered cutting section transitions smoothly from a diameter of 22.25 mm at the tip to 24.40 mm at the base. The standard itself ASME B94.2 specifies the dimensions of the reamer, not the thread — compatibility with NPT and Rc threads results from the 1:16 taper geometry itself.
In a threaded pipe connection, the taper provides the seal — the threads press increasingly tightly together as the connection is screwed in. If the thread were cut directly into a cylindrical hole, the pipe tap would have to form the taper and cut the thread profile simultaneously, significantly increasing torque and loading the first threads. The reamer forms the taper beforehand, so the tap only removes material to form the thread profile — evenly, with less resistance, producing a fuller, tighter-sealing thread and longer tap life.
Since the reamer produces only the 1:16 taper ratio, not the thread profile, the same hole can be tapped with different profiles sharing the same taper: NPT and NPTF (Dryseal, metal-to-metal seal, 60° profile), as well as Rc (taper pipe thread according to ISO 7-1, 55° profile). NPT is sometimes called the Briggs thread — after the author of the original standard.
Typical applications:
- Hydraulics and pneumatics — ports for fittings, valves and pressure connections
- Industrial fittings and piping systems — bodies, tees, reducers
- Maintenance and workshop use — repairing and restoring threaded ports
Making a 3/4" NPT thread step by step
Drilling → taper reaming → tapping
Three steps to a leak-tight pipe thread
1 Drilling the hole
Ø ~22.0 mm
2 Reaming 1:16
taper 22.25 → 24.40
3 Tapping
tap 3/4"-14 NPT
✓ Leak-tight connection
profile NPT / NPTF / Rc
Taper allowance: flute length 35 mm × taper ratio 1/16 = 2.19 mm increase in diameter (22.25 + 2.19 ≈ 24.40 mm). Thread pitch for 3/4"-14 NPT: 25.4 mm ÷ 14 = 1.81 mm.
3/4" NPT pipe thread parameters
Target thread data — for drill and tap selection
The values below describe the target thread 3/4"-14 NPT, for which the reamer prepares the hole — these are reference data for selecting the drill and tap, and not specifications of the reamer itself. The reamer determines only the taper ratio 1:16; the pitch, thread count and thread profile angle are produced by the tap.
| Thread / hole parameter | Value |
|---|---|
| Thread designation | 3/4"-14 NPT |
| Thread count | 14 threads per inch (TPI) |
| Thread pitch | 1.81 mm |
| Thread angle | 60° (NPT/NPTF) · 55° (Rc) |
| Taper ratio | 1:16 (3/4" per foot) — the only parameter produced by the reamer |
| Thread major Ø | ~26.7 mm (1.050") |
| Drill Ø with reaming | ~22.0 mm |
| Drill Ø without reaming | 59/64" ≈ 23.4 mm |
▲
Match the thread profile to the mating component
The reamer produces only the 1:16 taper ratio — it does not distinguish between thread profiles. Threads NPT (60°) and BSPT/R (55°) are not interchangeable despite having the same taper: they make only point contact and will not seal. The tap used after reaming must conform to the connection standard. The HSS tool is not intended for materials hardened above 40 HRC.
Taper ratio 1:16 — what it means in practice
a shallow taper for an NPT pipe thread
A taper ratio of 1:16 means that for every 16 mm of length, the diameter increases by 1 mm (in imperial units: 3/4 inch per foot). This is a shallow taper — to the naked eye, the tool looks almost cylindrical. Along the 35-millimeter cutting section, the diameter increases from Ø 22.25 mm at the tip (d₁) to Ø 24.40 mm at the base (d₂); the included taper angle is just 3.58°. NPT threads have the same taper — so the reamer prepares the hole precisely for this profile.
Frequently asked questions
Drill the pilot hole with a drill diameter close to the reamer tip diameter, approximately 22.0 mm (just under 22.25 mm). This allows the reamer to produce a 1:16 taper over its entire 35-millimeter flute length. If tapping without a reamer, use a larger 59/64" drill (≈ 23.4 mm) — the tap itself then forms the taper.
Yes. All three threads have the same taper 1:16, and the reamer only produces this taper. The thread profile (NPT and NPTF 60°, Rc 55°) is subsequently formed by the tap. However, finished NPT and Rc/BSPT connections are not interchangeable.
In a cylindrical hole, a taper pipe tap would have to form the taper and cut the thread simultaneously, significantly increasing torque and loading the first threads. Preliminary reaming reduces cutting resistance, improves thread concentricity and sealing, and extends tap life — especially in thick-walled housings and harder steels.
The version HSS (grade M2) works well in structural and carbon steel, cast iron, and nonferrous metals (brass, bronze, aluminum) — typical materials for valve bodies. In stainless steel and difficult-to-machine alloys, the cobalt version offers longer tool life HSS-Co (M35). Work by hand, steadily, using tapping oil; HSS is not intended for materials hardened above 40 HRC.
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