UNF: the American fine thread
UNF is the fine series of the Unified system and is used wherever a bolted joint needs more preload for less tightening travel or must not work loose under vibration: in engines, in hydraulics, on chassis parts. VÖLKEL makes 183 hand taps for it to DIN 2181 in HSS-G, from UNF No. 0 x 80 to UNF 2.1/2 x 12.
When UNF rather than UNC
At the same diameter UNF has more threads, hence a larger stress area and a smaller pitch. In practice that means higher load capacity, finer adjustment and better resistance to self-loosening. The price is a more delicate contour and more turns during assembly. In thin-walled parts UNF is the better choice, in soft materials such as aluminium and cast iron rather UNC.
Two tools are enough
The set is two-piece: a taper tap with a six to eight thread lead and a bottoming tap with two to three. There is no second tap, because a fine pitch removes less material per thread. On the shank you can tell them apart by one ring or no ring.
The designation
In 1/4-28 UNF, 1/4 is the outside diameter in inches and 28 the number of threads per inch. Below 1/4 inch, numbers replace fractions, from No. 0 at 0.060 inch upwards. Only UNEF is finer still.
Left-hand versions under UNF left hand, machine versions under UNF machine taps, complete imperial sets under UNC and UNF, tap drill sizes in the article calculate tap drill size.
All sizes at a glance
183 articles in 2 series. The article number links straight to the tool.
Hand Tap ISO 529 HSS-G
Hand Tap DIN 2181 HSS-G
| Threadnominal size | Tapping drillØ in mm | set of 2 pieces | Rougher | Finisher |
|---|---|---|---|---|
| UNF No. 0 x 80 | 1.3 | 24300 | 24300-1 | 24300-3 |
| UNF No. 1 x 72 | 1.6 | 24301 | 24301-1 | 24301-3 |
| UNF No. 2 x 64 | 1.9 | 24302 | 24302-1 | 24302-3 |
| UNF No. 3 x 56 | 2.1 | 24303 | 24303-1 | 24303-3 |
| UNF No. 4 x 48 | 2.4 | 24304 | 24304-1 | 24304-3 |
| UNF No. 5 x 44 | 2.7 | 24305 | 24305-1 | 24305-3 |
| UNF No. 6 x 40 | 3 | 24306 | 24306-1 | 24306-3 |
| UNF No. 8 x 36 | 3.5 | 24308 | 24308-1 | 24308-3 |
| UNF No. 10 x 32 | 4.1 | 24310 | 24310-1 | 24310-3 |
| UNF No. 12 x 28 | 4.7 | 24312 | 24312-1 | 24312-3 |
| UNF 1/4 x 28 | 5.5 | 24314 | 24314-1 | 24314-3 |
| UNF 5/16 x 24 | 6.9 | 24316 | 24316-1 | 24316-3 |
| UNF 3/8 x 24 | 8.5 | 24318 | 24318-1 | 24318-3 |
| UNF 7/16 x 20 | 9.9 | 24320 | 24320-1 | 24320-3 |
| UNF 1/2 x 20 | 11.5 | 24322 | 24322-1 | 24322-3 |
| UNF 9/16 x 18 | 12.9 | 24324 | 24324-1 | 24324-3 |
| UNF 5/8 x 18 | 14.5 | 24326 | 24326-1 | 24326-3 |
| UNF 3/4 x 16 | 17.5 | 24330 | 24330-1 | 24330-3 |
| UNF 7/8 x 14 | 20.25 | 24334 | 24334-1 | 24334-3 |
| UNF 1" x 12 | 23.25 | 24338 | 24338-1 | 24338-3 |
| UNF 1" x 14 | – | 24340 | 24340-1 | 24340-3 |
| UNF 1.1/8 x 12 | 26.5 | 24342 | 24342-1 | 24342-3 |
| UNF 1.1/4 x 12 | 29.5 | 24346 | 24346-1 | 24346-3 |
| UNF 1.3/8 x 12 | 32.5 | 24350 | 24350-1 | 24350-3 |
| UNF 1.1/2 x 12 | 36 | 24354 | 24354-1 | 24354-3 |
Tapping drill: drill diameter recommended by VÖLKEL (Technical Information “Tapping drill sizes”).
