Left-hand UNF threads
The combination of imperial thread, fine pitch and left-hand helix is the rarest on the shelf, and exactly for that reason hard to source when you need it. VÖLKEL makes 73 hand taps for left-hand UNF to DIN 2181 in HSS-G, as two-piece sets and as individual taps, from UNF No. 10 x 32 LH to UNF 1" x 12 LH.
Two tools, because it is a fine thread
As with right-hand UNF, the set consists of taper tap and bottoming tap. There is no second tap, because a fine pitch removes less material per thread. The coarse UNC left hand series keeps three tools.
Where these threads are found
Left-hand fine threads do two jobs: they hold where the direction of rotation in service would loosen a right-hand thread, and they prevent mix-ups on connections that must not be swapped. Both occur on clamping fixtures, on shaft ends and on fittings.
While working
Cut anticlockwise, reverse clockwise. A fine pitch also means more turns to depth, more friction and a greater need for lubrication. Suitable products are under lubricants. Tap drill sizes are in the article calculate tap drill size, the signs of left-hand threads in the article identify and cut left-hand threads correctly.
All sizes at a glance
73 articles in 2 series. The article number links straight to the tool.
Hand Tap ISO 529 HSS-G left hand thread
| Threadnominal size | Tapping drillØ in mm | set of 3 pieces | Taper Form A | Bottoming Form C | Second Form D |
|---|---|---|---|---|---|
| UNF 1/4 x 28 LH | 5.5 | 82350 | 82350-1 | 82350-3 | 82350-2 |
| UNF 5/16 x 24 LH | 6.9 | 82351 | 82351-1 | 82351-3 | 82351-2 |
| UNF 3/8 x 24 LH | 8.5 | 82352 | 82352-1 | 82352-3 | 82352-2 |
| UNF 7/16 x 20 LH | 9.9 | 82353 | 82353-1 | 82353-3 | 82353-2 |
| UNF 1/2 x 20 LH | 11.5 | 82354 | 82354-1 | 82354-3 | 82354-2 |
| UNF 9/16 x 18 LH | 12.9 | 82355 | 82355-1 | 82355-3 | 82355-2 |
| UNF 5/8 x 18 LH | 14.5 | 82356 | 82356-1 | 82356-3 | 82356-2 |
| UNF 3/4 x 16 LH | 17.5 | 82357 | 82357-1 | 82357-3 | 82357-2 |
| UNF 7/8 x 14 LH | 20.25 | 82358 | 82358-1 | 82358-3 | 82358-2 |
| UNF 1" x 12 LH | 23.25 | 82359 | 82359-1 | 82359-3 | 82359-2 |
Hand Tap DIN 2181 HSS-G left hand thread
| Threadnominal size | Tapping drillØ in mm | set of 2 pieces | Rougher | Finisher |
|---|---|---|---|---|
| UNF No. 10 x 32 LH | 4.1 | 24010 | 24010-1 | 24010-3 |
| UNF 1/4 x 28 LH | 5.5 | 24014 | 24014-1 | 24014-3 |
| UNF 5/16 x 24 LH | 6.9 | 24016 | 24016-1 | 24016-3 |
| UNF 3/8 x 24 LH | 8.5 | 24018 | 24018-1 | 24018-3 |
| UNF 7/16 x 20 LH | 9.9 | 24020 | 24020-1 | 24020-3 |
| UNF 1/2 x 20 LH | 11.5 | 24022 | 24022-1 | 24022-3 |
| UNF 9/16 x 18 LH | 12.9 | 24024 | 24024-1 | 24024-3 |
| UNF 5/8 x 18 LH | 14.5 | 24026 | 24026-1 | 24026-3 |
| UNF 3/4 x 16 LH | 17.5 | 24030 | 24030-1 | 24030-3 |
| UNF 7/8 x 14 LH | 20.25 | 24034 | 24034-1 | 24034-3 |
| UNF 1" x 12 LH | 23.25 | 24038 | 24038-1 | 24038-3 |
Tapping drill: drill diameter recommended by VÖLKEL (Technical Information “Tapping drill sizes”).
