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Description
Material HSS
Thread size M12 left
Number of pieces3 pcs
Tolerance 6H ISO2
Technical data for the M12 left-hand hand tap
| Technical data | |
|---|---|
| Thread Diameter d1 | M12 |
| Thread Pitch P | 1.75 mm |
| Overall Length l1 | 75 mm |
| Flute Length l2 | 24 mm |
| Shank Diameter d2 | 8 mm |
| Square Drive Width Across Flats a | 7 mm |
| Tap Drill Hole | 10.2 mm |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The M12 x1.75 LH thread is formed in the wall of a hole with a diameter of 10.2 mm. The thread groove extends 0.9 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 M12 LH hole – sequence 1, 2, 3
Hand tapping step by step
Thread M12 x1.75 LH in five steps
ØDrilling
Drill bit 10.2 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 12 mm minus pitch 1.75 mm gives 10.25 mm — in practice, use a 10.2 mm drill bit. 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 18 mm, or 1.5 times the thread diameter (1.5 x 12 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 M12 LH screw.
M12 left-hand HSS hand tap DIN 352 – 3-piece set for left-hand threads
The M12 left-hand hand tap set is a professional set of two tools for cutting internal left-hand threads with a diameter of 12 mm and a pitch of 1.75 mm. M12 left-hand HSS hand taps are used in machine drives, spindles, and industrial mechanisms where heavy loads require protection against threaded connections loosening on their own.
Key benefits of the M12 left-hand tap set
- 2-piece set (roughing and finishing taps) – an efficient solution for medium-sized left-hand threads
- M12 left-hand thread – used in lead screws, machine tool spindles, and drive components
- HSS high-speed steel – enables machining of structural and alloy steels with tensile strengths up to 800 MPa
- Tolerance 6H according to DIN 352 – precise fit with tolerance class 6g left-hand screws and nuts
- Popular industrial diameter – M12 left-hand fasteners are readily available on the market
The M12 left-hand hand tap set is suitable for manufacturing plants, machine tool service shops, and industrial machinery repair companies. To drill the tap hole for an M12 left-hand thread, use a drill bit with a diameter of 10.2 mm. Use tapping oil and remember to turn 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
Use a 10.2 mm drill bit for an M12 thread with a pitch of 1.75 mm. The diameter is identical to that for a right-hand thread.
A 2-piece set speeds up the work and is sufficient for most applications. For very hard materials or deep holes, a 3-piece set is a better choice.
M12 left-hand threads are found in machine tool spindles, lead screws, and machine drives. They protect threaded connections against loosening during operation.
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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