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Description
Material HSS
Thread size M27 left
Number of pieces3 pcs
Tolerance 6H ISO2
Technical data for the M27 left-hand hand tap
| Technical data | |
|---|---|
| Thread Diameter d1 | M27 |
| Thread Pitch P | 3 mm |
| Overall Length l1 | 110 mm |
| Flute Length l2 | 36 mm |
| Shank Diameter d2 | 20 mm |
| Square Drive Width Across Flats a | 16 mm |
| Tap Drill Hole | 24 mm |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The M27 x3 LH thread is formed in the wall of a hole with a diameter of 24 mm. The thread groove extends 1.5 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 M27 LH hole – sequence 1, 2, 3
Hand tapping step by step
Thread M27 x3 LH in five steps
ØDrilling
Drill bit 24 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 27 mm minus pitch 3 mm gives 24 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 40.5 mm, or 1.5 times the thread diameter (1.5 x 27 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 M27 LH screw.
M27 left-hand HSS hand tap – 3-piece set for left-hand threads
The M27 left-hand hand tap set is a specialized 3-piece HSS set for producing left-hand internal threads with a diameter of 27 mm. The M27 left-hand tap set includes a taper tap, a plug tap, and a bottoming tap, ensuring precise and controlled cutting of threads in the direction opposite to standard threads.
Key advantages of the M27 left-hand tap set
- M27 left-hand thread – used in mechanisms requiring protection against self-loosening
- HSS high-speed steel – a proven material with a hardness of 64 HRC for machining structural and alloy steels
- DIN 352 – an international standard ensuring tool dimensional repeatability and quality
- Tolerance class 6H – general-purpose thread accuracy for machinery and industrial applications
- Specialized applications – machine tool spindles, left-hand drives, gas connections, differential mechanisms
M27 left-hand taps are essential wherever a thread with the opposite direction to standard threads is required. The M27 left-hand tap set is chosen by specialists in the machinery and energy industries. Order the set and create connections resistant to self-loosening.
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
An M27 thread with a pitch of 3 mm requires a hole diameter of 24 mm. The size is identical for right-hand and left-hand versions of the thread.
A left-hand tap rotates counterclockwise. The operating technique remains the same as for a right-hand thread.
M27 left-hand threads are used in machine tool spindles, gas cylinders, drive mechanisms, and components that prevent loosening.
Product accessories
Metal drill bit 24 NWKc HSS DIN 345 Baildon
Reference: 0381 In stock > 10 items
€25.79
€31.72 brutto
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| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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