Polski 
- 98% satisfied customers
- 72h delivery
- 30 dni na zwrot
Description
Technical data for the American UNEF 7/8-20 hand tap
| Technical data | ||
|---|---|---|
| Nominal diameter d1 inches/mm | 7/8" | 22.22 mm |
| Thread pitch P inches/mm | 20 threads per inch | 1.27 mm |
| Overall length l1 | 80 mm | |
| Flute length l2 | 22 mm | |
| Shank diameter d2 | 18 mm | |
| Square drive size a | 14.5 mm | |
| Tap drill diameter | 21 mm | |
| Form C chamfer | (2÷3) P | |
| Thread angle G | 60° | |
| Thread standard | UNEF DIN 2184 | |
Roughing tap and finishing tap – how much material each removes
Division of work in the 1–2 set
The UNEF 7/8-20 thread is cut into the wall of a hole with a diameter of 21 mm. The thread groove extends 0.61 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 two passes.
The drawing shows the entire set in operation. Both taps have the same shank and the same length. They differ in their chamfer, the tapered tip: No. 1 has a chamfer spanning 8 threads, while No. 2 spans only 2 threads. The detail windows at the hole wall show how the thread groove deepens after each tap.
| Tap | Chamfer | Chamfer angle | Material removed | How it works in the hole |
|---|---|---|---|---|
| No. 1 – roughing tap | long, 8 threads | 5° | the main portion of the groove | enters smoothly and establishes thread alignment |
| No. 2 – finishing tap | short, 2 threads | 20° | the remainder, to the full profile | screws into the cut threads and produces the full 2B profile |
How to distinguish the taps in the set
The chamfer on No. 1 is 4 times as long as the chamfer on No. 2 — the difference is immediately visible when you place them side by side. No. 1 has an incomplete thread profile; only No. 2 has the full profile. The number is also indicated on the shank: No. 1 has one ring, No. 2 has none. Keep the set together and always start with the roughing tap.
How to tap a UNEF 7/8-20 hole – sequence 1, 2
Hand tapping step by step
Thread UNEF 7/8-20 in four steps
ØDrilling
Drill bit 21 mm
1Roughing tap
Chamfer 8 threads
2Finishing tap
Chamfer 2 threads
✓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 : 20 threads = 1.27 mm. The diameter of a UNEF 7/8-20 thread is 7/8 inch, or 22.22 mm. A diameter of 22.22 mm minus a pitch of 1.27 mm gives 20.95 mm — in practice, use a 21 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 55.6 mm, or 2.5 times the thread diameter (2.5 x 22.22 mm, shown as 2.5D in the drawing). Drill the hole deeper than the thread. The finishing tap has a chamfer spanning 2 threads, so approx. 2 incomplete threads remain near the bottom. The extra depth below the thread accommodates them along with the chips.
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 – the finishing tap produces the full profile
Unscrew the roughing tap and remove the chips from the hole. Screw the finishing tap into the cut threads by hand – it should engage them naturally. Continue turning at the same rhythm as with the roughing tap. The finishing tap removes the remaining material and cuts the groove to the full profile within tolerance 2B. When it screws in smoothly all the way, the thread is ready – check it with a UNEF 7/8-20 screw.
UNEF 7/8-20 Fine-Thread Hand Tap Set
Hand Tap UNEF 7/8-20 is designed for precision cutting of internal threads in the series UNEF (Unified National Extra Fine thread series) in applications with short engagement lengths and thin-walled housings; the thread profile is 60°, and the fine pitch of 20 TPI provides high thread density and stable tightening torque adjustment.
- Repeatable profile geometry — the precise 60° profile reduces burrs and improves surface roughness at the exit.
- Lower cutting torque — the ground cutting edge and optimized rake angle promote smooth guidance in blind and through holes.
- Stability in thin-walled parts — the fine pitch of 20 TPI increases pull-out load capacity where engagement length is limited.
Hand Tap Set UNEF 7/8-20 provides a repeatable fine-thread profile for precision connections in systems requiring high thread density and short engagement lengths.
Frequently asked questions
UNEF (Unified National Extra Fine thread series) is a fine-thread variant of the American system with a 60° profile and an increased number of threads per inch. It is used where engagement length is short or walls are thin — most commonly in pipe connections, hydraulic and pneumatic fittings, measuring equipment, and precision fasteners — to increase pull-out resistance and allow very fine adjustment.
Product accessories
Reviews
No customer reviews for the moment.
Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| 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 |
Recommended for you
This website uses its own and third-party cookies to improve our services and show you advertising related to your preferences by analyzing your browsing habits. To give your consent to its use, press the Accept button.
Cookie preferences
Functional cookiesTechnical
Functional cookies are strictly necessary to provide the services of the shop, as well as for its proper functioning, so it is not possible to refuse their use. They allow the user to browse through our website and use the different options or services that exist on it.
Advertising Cookies
These are cookies that collect information about the advertisements shown to users of the website. They can be anonymous, if they only collect information about the advertising spaces shown without identifying the user, or personalised, if they collect personal information about the user of the shop by a third party, for the personalisation of these advertising spaces.
Analytics cookies
Collect information about the user's browsing experience in the shop, usually anonymously, although sometimes they also allow the user to be uniquely and unequivocally identified in order to obtain reports on the user's interests in the products or services offered by the shop.