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Description
Material HSS
Thread size M18 left
Number of pieces3 pcs
Tolerance 6H ISO2
Technical data for the M18 left-hand hand tap
| Technical data | |
|---|---|
| Thread Diameter d1 | M18 |
| Thread Pitch P | 2.5 mm |
| Overall Length l1 | 95 mm |
| Flute Length l2 | 30 mm |
| Shank Diameter d2 | 14 mm |
| Square Drive Width Across Flats a | 11 mm |
| Tap Drill Hole | 15.5 mm |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The M18 x2.5 LH thread is formed in the wall of a hole with a diameter of 15.5 mm. The thread groove extends 1.25 mm into the wall. A single tap would have to cut the entire groove at once – by hand, this creates high resistance and a risk of breakage. The set divides this work into three layers.
The drawing shows the entire set in operation. All three taps have the same shank and the same length. They differ in chamfer length: No. 1 has a taper spanning 7–10 threads, while No. 3 spans only 1–2 threads. The detail views at the hole wall show how the thread groove deepens after each tap.
| Tap | Chamfer | Material removed | How it works in the hole |
|---|---|---|---|
| No. 1 – roughing tap | long, 7–10 threads | approx. 60% | enters smoothly and establishes thread alignment |
| No. 2 – intermediate | medium, 3–5 threads | approx. 30% | screws into the previously cut threads and starts cutting only deeper in the hole |
| No. 3 – finishing tap | short, 1–2 threads | approx. 10% + sizing | turns easily and produces the full 6H profile |
How to identify the tap numbers in the set
The chamfer is the tapered end of the tap. No. 1 has the longest chamfer and No. 3 the shortest – the difference is immediately visible when they are placed side by side. No. 1 and No. 2 have shallower thread profiles; only No. 3 has the full profile. The number can also be identified on the shank: No. 1 has one ring, No. 2 has two, and No. 3 has none. Keep the set together and always start with the roughing tap.
How to tap an M18 LH hole – sequence 1, 2, 3
Hand tapping step by step
Thread M18 x2.5 LH in five steps
ØDrilling
Drill bit 15.5 mm
1Roughing tap
Removes approx. 60%
2Intermediate
Removes approx. 30%
3Finishing tap
Removes approx. 10%
✓Finished thread
Tolerance 6H
Turning sequence: half a turn counterclockwise, a quarter turn clockwise | Between taps: remove chips from the hole
Start with the hole. The drill diameter is easy to calculate: thread diameter 18 mm minus pitch 2.5 mm gives 15.5 mm. An undersized hole is a common cause of a tap twisting off in the workpiece.
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 27 mm, or 1.5 times the thread diameter (1.5 x 18 mm, shown as 1.5D in the drawing). Drill the hole deeper than the thread. The clearance below the thread accommodates chips and the finishing tap chamfer.
No. 1 – the roughing tap establishes thread alignment
Fit the roughing tap into a tap wrench and position it perpendicular to the surface. Check the angle from two sides, for example with a square. This is a left-hand thread, so turn in the opposite direction to usual: half a turn counterclockwise, then a quarter turn clockwise. Reversing breaks the chip into short pieces — a slight crunch is normal. The first threads determine whether the thread will be straight.
No. 2 and No. 3 – deepening and full profile
Unscrew the roughing tap and remove chips from the hole. Screw the intermediate tap by hand into the previously cut threads – it should engage them naturally. It turns easily at first and starts cutting only deeper in the hole. The finishing tap enters with almost no resistance and cuts the final portion of the profile only at the end. When it screws smoothly all the way in, the thread is ready – check it with an M18 LH screw.
M18 left-hand HSS hand tap DIN 352 – 3-piece set for heavy industry
The M18 left-hand hand tap set is a professional set of three tools for producing internal left-hand threads with a diameter of 18 mm and a pitch of 2.5 mm. M18 left-hand HSS hand taps are designed for industrial applications where large diameters and left-hand threads are dictated by the design requirements of machinery and equipment.
Key benefits of the M18 left-hand tap set
- 3-piece set (roughing, intermediate, and finishing taps) – essential for large diameters where the tool load is substantial
- M18 left-hand thread – used in mining machinery, metallurgical equipment, and heavy construction equipment
- HSS high-speed steel – enables machining of carbon and low-alloy steels with tensile strengths up to 800 MPa
- 6H tolerance according to DIN 352 – guarantees proper fit with left-hand screws in tolerance class 6g
- Pitch 2.5 mm – ensures fast tapping progress while maintaining connection strength
The M18 left-hand hand tap set is suitable for heavy industry plants, mines, and construction machinery service companies. Use a drill bit with a diameter of 15.5 mm to prepare the hole for an M18 left-hand thread. Such a large diameter requires a sturdy tap wrench and secure clamping of the workpiece.
Tolerance 6H — metric thread tolerance classes
| Class | Accuracy | Application | Status |
|---|---|---|---|
| 4H / 4g | High | Precision connections, hydraulics | — |
| 6H / 6g | Standard | Machine building, general-purpose | SELECTED |
| 7H / 8g | Low | Large clearance, easy assembly | — |
6H = internal thread (nut, hole) | 6g = external thread (screw)
Frequently asked questions
For an M18 thread with a 2.5 mm pitch, use a 15.5 mm drill. Formula: diameter minus pitch (18 - 2.5 = 15.5 mm).
The large diameter and 2.5 mm pitch generate substantial cutting forces. Three taps distribute the work and protect the tools against overload and breakage.
The M18 tap requires a large tap wrench with a range of 8-20 mm or size 4. The square shank measures approximately 14 mm.
Product accessories
HSSE 15.5 cobalt metal drill bit DIN 338
Reference: 13293 In stock < 10 items
€15.26
€18.77 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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