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Description
Technical data for the UNF No4-48 hand tap
| Technical data | ||
|---|---|---|
| Nominal Diameter d1 Inches/mm/Decimal | UNF No4-48 | |
| Thread Pitch P in Inches and mm | 48 threads per inch | 0.53 mm |
| Thread Diameter d1 mm / Decimal | 2.84 mm / 0.1120 in | |
| Thread angle G | 60° | |
| Thread Standard | UNF ANSI B-1.1 | |
| Overall Length l1 | 40 mm | |
| Flute Length l2 | 10 mm | |
| Shank Diameter d2 | 3.5 mm | |
| Square Drive Width Across Flats a | 2.7 mm | |
| Tap Drill Hole | 2.3 mm | |
Roughing, intermediate, and finishing taps – how much material each removes
Division of work in the 1–2–3 set
The UNF No 4-48 thread is cut into the wall of a 2.3 mm diameter hole. The thread groove extends 0.27 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. Keep the set together and always start with the roughing tap.
How to tap a UNF No 4-48 hole – sequence 1, 2, 3
Hand tapping step by step
Thread UNF No 4-48 in five steps
ØDrilling
Drill bit 2.3 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 is 25.4 mm, and 25.4 ÷ 48 threads ≈ 0.53 mm. The UNF No 4-48 thread diameter is 0.112 inches, or 2.84 mm. Subtracting the 0.53 mm pitch from the 2.84 mm diameter gives 2.31 mm – in practice, use a 2.3 mm drill bit. An undersized hole is a common cause of taps twisting off in the material.
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 4.3 mm, or 1.5 times the thread diameter (1.5 x 2.84 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 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 only starts cutting deeper in the hole. The finishing tap enters with almost no resistance and only cuts the final portion of the profile at the end. Once it screws in smoothly all the way, the thread is ready – check it with a UNF No 4-48 screw.
UNF No 4-48 hand tap – set of 3 taps for miniature fine threads
UNF No 4-48 hand tap is a three-piece set of precision tools for cutting internal threads to the Unified National Fine – UNF standard. The set includes HSS roughing, intermediate, and finishing taps and complies with DIN 2181.
UNF No 4-48 tap characteristics
- Three-piece set – progressive cutting minimizes the risk of breaking the delicate tool
- Miniature diameter No 4 (2.84 mm) – compact size for small components
- 48 threads per inch (0.53 mm pitch) – fine thread profile resists loosening under vibration
- UNF standard – unified fine thread for precision engineering
- HSS high-speed steel – machining of nonferrous metals and plastics up to 800 MPa
The UNF No 4-48 thread is found in precision electronics, measuring instruments, and mechanisms requiring vibration resistance. UNF No 4-48 miniature tap is selected by service shops repairing medical equipment, optical equipment, and precision measuring instruments.
Frequently asked questions
Calculate the hole diameter using the formula: d = D - P. For UNF No 4-48: d = 2.84 mm - 0.53 mm = 2.31 mm. Use a 2.3 mm drill bit for proper tapping.
Both threads have a No 4 diameter (2.84 mm), but differ in pitch. UNF No 4-48 has 48 threads per inch (0.53 mm pitch), while UNC No 4-40 has only 40 threads per inch (0.64 mm pitch). The UNF version is finer and holds better under vibration.
You need a caliper and a thread pitch gauge. External thread (on a shaft): measure the major diameter – it should be 2.84 mm (No 4). Internal thread (in a hole): measure the hole diameter – it should be approximately 2.3 mm. Then place the thread pitch gauge against the threads – the 48 TPI leaf fits this thread. The 60° thread angle confirms the American standard.
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