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Description
Technical data for the American UNEF 5/16-32 hand tap
| Technical data | ||
|---|---|---|
| Nominal diameter d1 inches/mm | 5/16" | 7.93 mm |
| Thread pitch P inches/mm | 32 threads per inch | 0.79 mm |
| Overall length l1 | 56 mm | |
| Flute length l2 | 18 mm | |
| Shank diameter d2 | 6 mm | |
| Square drive size a | 4.9 mm | |
| Tap drill diameter | 7.15 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 5/16-32 thread is cut into the wall of a hole with a diameter of 7.15 mm. The thread groove extends 0.395 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 5/16-32 hole – sequence 1, 2
Hand tapping step by step
Thread UNEF 5/16-32 in four steps
ØDrilling
Drill bit 7.15 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 : 32 threads ≈ 0.79 mm. The diameter of a UNEF 5/16-32 thread is 5/16 inch, or 7.94 mm. A diameter of 7.94 mm minus a pitch of 0.79 mm gives 7.15 mm. 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 19.9 mm, or 2.5 times the thread diameter (2.5 x 7.94 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 5/16-32 screw.
UNEF 5/16-32 Fine-Thread Hand Tap Set
Hand Tap UNEF 5/16-32 is used to produce precision internal threads in the system UNEF (Unified National Extra Fine), used where engagement length is limited and in thin-walled housings; the characteristic 60° profile meets the requirements of the thread American fine-thread.
HSS construction with ground flute geometry promotes smooth hand operation and even guidance in blind and through holes. The pitch of 32 TPI provides high thread density and stable adjustment, while suitable lubricants and periodic reversal facilitate chip breaking and protect the cutting edges. Quality is checked with a GO/NO-GO thread plug gauge for a target class 2B fit.
- Precise 60° geometry — a clean profile with fewer burrs at the exit.
- Stable tapping process — the ground edge and chamfer reduce instantaneous cutting torque.
- Interchangeability and repeatability — a class 2B fit and GO/NO-GO inspection make it easier to maintain dimensional accuracy.
- Durability in service — HSS maintains cutting performance longer and improves tool life.
Hand Tap Set UNEF 5/16-32 provides a repeatable fine thread for connections requiring high thread density and predictable adjustment in thin-walled structures.
Frequently asked questions
UNEF (Unified National Extra Fine) is a fine-thread variant of the system American thread with a 60° profile and an increased number of threads per inch. It is selected where engagement length is limited or in thin-walled components — especially in pipe connections and hydraulic and pneumatic fittings, inspection and measuring equipment, and precision fasteners — when high pull-out resistance and very fine adjustment are required.
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