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Description
Material HSS
Thread size M20 left
Number of pieces3 pcs
Tolerance 6H ISO2
Technical data for the M20 left-hand hand tap
| Technical data | |
|---|---|
| Thread Diameter d1 | M20 |
| Thread Pitch P | 2.5 mm |
| Overall Length l1 | 95 mm |
| Flute Length l2 | 32 mm |
| Shank Diameter d2 | 16 mm |
| Square Drive Width Across Flats a | 12 mm |
| Tap Drill Hole | 17.5 mm |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The M20 x2.5 LH thread is formed in the wall of a hole with a diameter of 17.5 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 M20 LH hole – sequence 1, 2, 3
Hand tapping step by step
Thread M20 x2.5 LH in five steps
ØDrilling
Drill bit 17.5 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 20 mm minus pitch 2.5 mm gives 17.5 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 30 mm, or 1.5 times the thread diameter (1.5 x 20 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 M20 LH screw.
M20 left-hand HSS DIN 352 hand tap – 3-piece set for medium-sized left-hand threads
The M20 left-hand hand tap set is a professional set of three tools for cutting left-hand internal threads with a diameter of 20 mm and a pitch of 2.5 mm. M20 left-hand HSS hand taps conforming to DIN 352 are used in the machinery industry, automotive applications, and drive systems, where medium-sized left-hand threads prevent connections in rotating components from loosening.
Key benefits of the M20 left-hand tap set
- 3-piece set (roughing, intermediate, and finishing taps) – cutting in three stages distributes the load evenly
- M20 left-hand thread – secures connections in spindles, axles, and rotating hubs
- HSS high-speed steel – enables machining of steel, aluminum, and cast iron up to 800 MPa
- Tolerance 6H according to DIN 352 – a precise fit with M20 left-hand screws of tolerance class 6g
- Popular industrial diameter – frequently used in machines, vehicles, and technical equipment
The M20 left-hand hand tap set is suitable for machine manufacturing plants, automotive service centers, and companies working with drive systems. To drill the hole for an M20 left-hand thread, use a drill bit with a diameter of 17.5 mm. Remember – a left-hand tap turns counterclockwise.
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
A 17.5 mm drill bit is used for an M20 thread with a pitch of 2.5 mm. Formula: diameter minus pitch (20 - 2.5 = 17.5 mm).
M20 left-hand threads are used in wheel hubs, machine tool spindles, and vehicle axles, where they prevent loosening.
Yes, the tap wrench is the same. The difference is the direction of rotation – a left-hand tap turns to the left (counterclockwise).
Product accessories
HSSE 17.5 cobalt metal drill bit DIN 338
Reference: 13297 In stock > 10 items
€17.11
€21.04 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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