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Description
Technical data for the G 7/8 inch hand tap
| Technical data | ||
|---|---|---|
| Nominal diameter d1 inches/mm | G 7/8 in | 30.20 mm |
| Thread pitch P inches/mm | 14 threads per inch | 1.81 mm |
| Overall length l1 | 90 mm | |
| Flute length l2 | 22 mm | |
| Shank diameter d2 | 22 mm | |
| Square drive size a | 18.0 mm | |
| Tap drill diameter | 28.25 mm | |
| Form C chamfer | No. 1: 5P, No. 2: 2P | |
| Thread angle G | 55° | |
| Thread standard | BSP DIN ISO 228 | |
Roughing tap and finishing tap – how much material each removes
Division of work in the 1–2 set
The G 7/8 thread is cut into the wall of a hole with a diameter of 28.25 mm. The thread groove extends 0.98 mm into the wall. A single tap would have to cut the entire groove at once – by hand, this means high resistance and a risk of breakage. The set divides this work into two passes.
The drawing shows the entire set in operation. Both taps have the same shank and the same length. They differ in their chamfer, the tapered tip: No. 1 has a chamfer spanning 5 threads, while No. 2 spans only 2 threads. The detail windows at the hole wall show how the thread groove deepens after each tap.
| Tap | Chamfer | Chamfer angle | Material removed | How it works in the hole |
|---|---|---|---|---|
| No. 1 – roughing tap | long, 5 threads | 7° | the main portion of the groove | enters smoothly and establishes thread alignment |
| No. 2 – finishing tap | short, 2 threads | 20° | the remainder, to the full profile | screws into the previously cut threads and produces the full thread profile |
How to distinguish the taps in the set
The chamfer on No. 1 is 2.5 times as long as the chamfer on No. 2 – the difference is immediately visible when you place them side by side. No. 1 has an incomplete thread profile; only No. 2 has the full profile. The number is also indicated on the shank: No. 1 has one ring, No. 2 has none. Keep the set together and always start with the roughing tap.
How to tap a G 7/8 hole – sequence 1, 2
Hand tapping step by step
Thread G 7/8 in four steps
ØDrilling
Drill bit 28.25 mm
1Roughing tap
Chamfer 5 threads
2Finishing tap
Chamfer 2 threads
✓Finished thread
Thread G 7/8
Turning sequence: half a turn clockwise, a quarter turn counterclockwise | Between taps: remove chips from the hole
Start with the hole. The G thread has a Whitworth profile, with a thread height of 0.64 times the pitch. The minor diameter of the internal thread is the 30.201 mm diameter minus twice the thread height, or 1.28 × the 1.814 mm pitch: the result is 27.877 mm. ISO 228-1 permits a hole diameter from 27.877 to 28.418 mm, and a 28.25 mm drill falls within this range. An undersized hole is a common cause of taps twisting off in the material.
Through hole or blind hole – how deep to drill
The set taps both types of holes. In a through hole, the thread extends through the full material thickness. In a blind hole, cut the thread to match the thread length of the fitting being installed. Drill the hole deeper than the thread. The finishing tap has a 2-thread chamfer, so approximately 2 incomplete threads remain near the bottom. The extra depth below the thread accommodates these along with the chips.
No. 1 – the roughing tap establishes thread alignment
Fit the roughing tap in the tap wrench and position it perpendicular to the surface. Check the angle from two sides, for example with a square. Turn half a turn clockwise, then a quarter turn counterclockwise. Reversing breaks the chip into short pieces – a slight crunch is normal. The first threads determine whether the thread will be straight.
No. 2 – the finishing tap produces the full profile
Back out the roughing tap and remove chips from the hole. Screw the finishing tap by hand into the previously cut threads – it should engage them naturally. Continue turning with the same rhythm used for the roughing tap. The finishing tap removes the remaining material and cuts the groove to its full profile. When it screws in smoothly all the way, the thread is finished – check it with a G 7/8 thread plug gauge: the GO end screws in by hand over the full length, while the NO-GO end enters no more than 2 threads.
7/8 inch G pipe hand tap
Hand Tap 7/8 inch G DIN 5157/2 HSS Fwp is a professional 2-piece set (roughing tap + finishing tap) designed for manually cutting G pipe threads (BSP – British Standard Pipe) with a profile of 55°. Made of high-grade high-speed steel (HSS), it provides durability, abrasion resistance, and precision even when working in harder materials.
The tap, compliant with standard DIN 5157/2 is used to cut G7/8 inch parallel threads, with a major diameter of 30.291 mm (in accordance with ISO 228-1). The tool performs exceptionally well in installation, hydraulic, and pneumatic work, as well as in metalworking shops and technical service facilities.
7/8 inch pipe tap ensures safe, accurate thread cutting through staged machining – the roughing tap makes the initial cut, and the finishing tap completes the thread to full accuracy.
- 2-piece set DIN 5157/2 – roughing and finishing taps for full control over the tapping process.
- 55° thread profile – complies with the BSP (G) standard, ensuring excellent leak-tightness in pipe connections.
- G 7/8 inch thread diameter - 30.291 mm – complies with ISO 228-1.
- Material: high-speed steel (HSS) – abrasion-resistant, ideal for use in steel, brass, aluminum, and plastics.
- For manual applications – precise tool guidance in workshop and installation applications.
G 7/8 inch Hand Tap brand Fwp is a reliable tool for the everyday work of fitters, installers, and metalworkers. It guarantees dimensional repeatability, durability, and compliance with industrial standards for BSP threaded connections
.Stages of cutting a G 7/8 inch thread with a 2-piece set: roughing and finishing taps
Frequently asked questions
For this reason, always check the thread diameter in the technical data instead of converting inches directly to millimeters. In the BSP system, thread size is determined by the design of the entire installation, not just the nominal dimension.
No. The G (BSP) thread is a parallel pipe thread, which means its diameter is constant along its entire length. Unlike taper threads (designated R or BSPT), G-thread connections are not self-sealing. This means the G thread does not provide a seal on its own – it requires an additional sealing element, such as a flat gasket, an O-ring, or a plastic washer. This sealing method is commonly used in hydraulic, pneumatic, and industrial systems.
Product accessories
Tapered countersink 37/90 DIN 335 C HSS
Reference: 0000004108 In stock > 10 items
€32.11
€39.49 brutto
Metal drill bit 28.25 NWKc HSS DIN 345 Zbrojovka
Reference: 0394 In stock > 10 items
€38.42
€47.26 brutto
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