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Description
Technical data for the G 2 1/2 inch hand tap
| Technical data | ||
|---|---|---|
| Nominal diameter d1 inches/mm | G 2 1/2 inch | 75.18 mm |
| Thread pitch P inches/mm | 11 threads per inch | 2.309 mm |
| Overall length l1 | 160 mm | |
| Flute length l2 | 40 mm | |
| Shank diameter d2 | 50 mm | |
| Square drive size a | 39 mm | |
| Tap drill diameter | 72.54 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 2 1/2 thread is cut into the wall of a hole with a diameter of 72.54 mm. The thread groove extends 1.32 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 2 1/2 hole – sequence 1, 2
Hand tapping step by step
Thread G 2 1/2 in four steps
ØDrilling
Drill bit 72.54 mm
1Roughing tap
Chamfer 5 threads
2Finishing tap
Chamfer 2 threads
✓Finished thread
Thread G 2 1/2
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 75.184 mm diameter minus twice the thread height, or 1.28 × the 2.309 mm pitch: the result is 72.226 mm. ISO 228-1 permits a hole diameter from 72.226 to 72.866 mm, and a 72.54 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
Unscrew the roughing tap and remove the chips from the hole. Screw the finishing tap into the cut threads by hand – it should engage them naturally. Continue turning at the same rhythm as with 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 ready – check it with a G 2 1/2 thread plug gauge: the GO end screws in by hand over the full length, while the NO-GO end enters no more than 2 turns.
G 2 1/2 inch pipe hand tap
Hand Tap 2 1/2 inch G DIN 5157/2 HSS is a professional 2-piece set (roughing tap + finishing tap), designed for manually cutting G parallel pipe threads (BSP – British Standard Pipe) o a profile angle of 55°. The tool is made of high-grade high-speed steel (HSS), which provides high abrasion resistance and long tool life even in demanding industrial conditions.
The G 2 1/2 inch thread has an external diameter of 75.184 mm, in accordance with ISO 228-1. Thanks to geometry compliant with DIN 5157/2, the tap enables gradual, safe, and precise thread cutting in two stages – using a roughing tap and a finishing tap.
G 2 1/2 inch pipe tap is a reliable tool for installers, metalworkers, and maintenance personnel who make threaded connections in industrial, gas, water supply, and process systems.
- 2-piece set (DIN 5157/2) – roughing and finishing taps for precise hand tapping.
- G 2 1/2 inch thread – external diameter 75.184 mm (per ISO 228-1).
- 55° thread profile – complies with the BSP standard, ensuring leak-tightness and installation compatibility.
- Material: high-speed steel (HSS) – durable, wear-resistant, and designed for use in steel, brass, and plastics.
- Professional applications – in large installation and industrial systems.
Hand Tap 2 1/2 inch G DIN 5157/2 HSS is a tool designed for demanding users who need a precise, durable solution for large-diameter BSP threads.
Stages of cutting a G 2 1/2 inch thread with a 2-piece set: roughing and finishing taps
Frequently asked questions
The question “how many mm is G 2 1/2 inch” or “how many cm is G 2 1/2 inch” often arises when selecting pipe tapping tools. Contrary to what one might expect, the value 2 1/2 inch (equivalent to 75.18 mm or 7.52 cm) does not indicate the thread diameter, but the nominal size of the pipe that the thread fits. In practice, the 2 1/2 inch G tap has an outside diameter of 75.18 mm, because G (BSP) pipe threads are designed for thick-walled pipes.
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. A G (BSP) thread is a parallel pipe thread, meaning its diameter is constant along its entire length. Unlike taper threads (designated R or BSPT), G threaded connections are not self-sealing. This means that a G thread does not provide a seal on its own – it requires an additional sealing element, e.g. a flat gasket, O-ring or plastic washer. This sealing method is commonly used in hydraulic, pneumatic and industrial installations.
Product accessories
Countersink 2 1/2 inch G HSS DIN EN 24231 Cztool
Reference: 0000003736 In stock < 10 items
€210.53
€258.95 brutto
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