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Description
Technical data for the UNC 3/4-10 hand tap
| Technical data | ||
|---|---|---|
| Nominal Diameter d1 Inches/mm/Decimal | UNC 3/4-10 | |
| Thread Pitch P in Inches and mm | 10 threads per inch | 2.54 mm |
| Thread Diameter d1 mm / Decimal | 19.05 mm / 0.7500 in | |
| Thread angle G | 60° | |
| Thread Standard | UNC ANSI B-1.1 | |
| 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 | 16.5 mm | |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The UNC 3/4-10 thread is cut into the wall of a 16.5 mm diameter hole. The thread groove extends 1.275 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 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 2B 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 a UNC 3/4-10 hole – sequence 1, 2, 3
Hand tapping step by step
Thread UNC 3/4-10 in five steps
ØDrilling
Drill bit 16.5 mm
1Roughing tap
Removes approx. 60%
2Intermediate
Removes approx. 30%
3Finishing tap
Removes approx. 10%
✓Finished thread
Tolerance 2B
Turning sequence: half a turn clockwise, a quarter turn counterclockwise | Between taps: remove chips from the hole
Start with the hole. For inch threads, pitch is specified in threads per inch, so first convert it to millimeters: an inch equals 25.4 mm, and 25.4 : 10 threads = 2.54 mm. The diameter of the UNC 3/4-10 thread is 3/4 inch, or 19.05 mm. The diameter of 19.05 mm minus the pitch of 2.54 mm gives 16.51 mm – in practice, use a 16.5 mm drill bit. An undersized hole is a common cause of taps 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 28.6 mm, or 1.5 times the thread diameter (1.5 x 19.05 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 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 and No. 3 – deepening and full profile
Back out the roughing tap and remove the chips from the hole. Screw the intermediate tap into the cut threads by hand – 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 in smoothly all the way, the thread is complete – check it with a UNC 3/4-10 screw.
UNC 3/4-10 hand tap – set of 3 pcs for large coarse threads
UNC 3/4-10 hand tap is a three-piece set of professional tools for cutting large-diameter internal Unified National Coarse – UNC threads. The set includes HSS roughing, intermediate, and finishing taps manufactured to DIN 352.
Features of the UNC 3/4-10 tap
- Class 2B tolerance – standard accuracy for heavy-duty industrial connections
- Large diameter of 3/4 inch (19.05 mm) – designed for connections carrying substantial loads
- 10 threads per inch (2.54 mm pitch) – coarse thread profile for fast assembly
- Three-tap system – distributing the cutting load protects the tools from overload
- HSS high-speed steel – efficient machining of structural steels up to 800 MPa
The UNC 3/4-10 thread is used in American-made heavy construction equipment, steel structures, and industrial machinery. UNC 3/4-10 coarse-thread tap is chosen by workshops servicing Caterpillar and John Deere machines and steel structures built to American standards.
Frequently asked questions
Calculate the hole diameter using the formula: d = D - P. For UNC 3/4-10: d = 19.05 mm - 2.54 mm = 16.51 mm. Use a 16.5 mm drill bit before starting to tap.
Both threads have a diameter of 3/4 inch (19.05 mm), but differ in pitch. UNC 3/4-10 has 10 threads per inch, while UNF 3/4-16 has as many as 16 threads per inch. UNC is coarser and quicker to assemble, while UNF provides better sealing.
You need a caliper and a thread pitch gauge. External thread (on a shaft): measure the outside diameter; it should be 19.05 mm (3/4 in). Internal thread (in a hole): measure the hole diameter; it should be approximately 16.5 mm. Then place the thread pitch gauge against the threads; the 10 TPI leaf fits this thread. The 60° thread angle confirms the American standard.
Product accessories
HSSE 16.5 cobalt metal drill bit DIN 338
Reference: 13295 In stock < 10 items
€17.63
€21.69 brutto
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