Grip - imperial threading question

So far I had only to do with imperial threads as an end user
But now I have several lighting tripods and a slider with some damaged threads and decided to repair them by re-cutting. In the past I had done this with metric threads only and I am a bit lost with the English imperial system.

I need to re-cut 1/4" and 3/8" threads. I learned that there are UNC, UNF, UNEF, NPT, BSW, BSF, and G threads. I have no idea what type on lighting grip is used.

I'd like to buy a high quality set (German made preferred; like RUKO or Völkel) - so if someone can point me into the right place on Amazon? What are the correct English terms for those tools?

Thanks for your help!

I believe UNC is the standard thread to use for imperial sizes...for 1/4 inch its 20 TPI (hence the 1/4 20 designation) and for 3/8's its 16 tpi

Thanks, Stu!

The taps I have are marked 1/4 20 UNC (meaning that they are 1/4 inch in diameter and have 20 threads per inch) for modern tripod thread and 3/8 16 UNC for previous bigger tripod thread. Also I have 5/8 11 UNC taps but they are used in geodetic tripods only.

Hi Robert,
Unfortunately there are a lot of thread sizes and it is also easy enough to make non-standard sizes which complicates the issue further. The common camera mount threads (as has been mentioned) are ¼” 20 tpi (threads per inch) and 3/8” 16tpi. These are the standards for BSW (British Standard Whitworth) and UNC (Unified National Coarse). BSW uses a 55 degree thread angle whereas UNC uses 60 degree. Despite the different angles they are mostly interchangeable except for ½’’ where the tpi differ.

If you are wanting to repair threads there are ways of repairing light damage without using a tap or die. If not too severe is maybe possible to remove deformations with a triangular or other fine file. There are also files made for repairing threads.

I do a bit of metalwork including thread cutting mostly using taps and dies but I also use a screw cutting lathe. Often the requirement is to make a male thread in aluminium to fit a female aluminium thread. This combination is very likely to seize if the thread is even a little too tight. A way to prevent this is to coat the surfaces before testing with a metal polish (a paste works well) and to gently work the parts together - backing off at any sign of binding. I have had a lot of success using metal polish and would not attempt an aluminium to aluminium combination without it.

If the damage is severe and a tap or die is required a thread gauge can very useful for measuring the pitch. Some times the length of thread available is too short for effective gauge use – a lens cap for example. In this case it may be possible to measure how far the cap moves with every rotation. One you have the pitch and diameter you can look up the thread charts to see if it is a standard and then decide whether to buy a tap or die.

Thanks guys, especially Alastair for your very in depth information. Very helpful.

I have several light stands which have been been damaged by Kinoflo Divalites because the tightening screw of the mount sits too high and presses directly into the thread of the light stand spigot.
I only realized the damage when I used the light stands for my Kessler Pocket Dolly - of course after I had damaged the threads of the slider, too.

I was planning to buy a metric tap set anyway and would add UNC 3/8 and 1/4 for that kind of repair work. I had done a lot of metal work during my technical engineering school time in the 90ies, but have forgotten a lot of that stuff.

If you are wanting to repair threads there are ways of repairing light damage without using a tap or die. If not too severe is maybe possible to remove deformations with a triangular or other fine file. There are also files made for repairing threads.

Unfortunately it's quite possible that damage is too big to be re-cut. (For instance, I have a tripod with a damaged nut which could only be replaced). So it may be simpler to cut a new 3/8 threaded hole and glue inside it a 3/8 to 1/4 adapter available on Ebay.

If you have damaged internal threads you might want to get some thread repair kits. Search for "Helicoil" on eBay and Youtube!

If I remember correctly 1/4 Whitworth (BSW) is the standard tripod thread.

Steve

So, finally after a long time and with a few failed purchases I got the right stuff together.

Quoting Wikipedia about tripod thread standards:

Screw thread
Per ISO 1222:2010,[1] the current tripod screw thread standard for attaching the camera calls for a 1/4-20 UNC[2] or 3/8-16 UNC thread.[3] Most consumer cameras are fitted with 1/4-20 UNC threads. Larger, professional cameras and lenses may be fitted with 3/8-16 UNC threads, plus a removable 1/4-20 UNC adapter, allowing them to be mounted on a tripod using either standard.

Historically, The Royal Photographic Society recommended the thread standard for attaching older cameras to tripods was 3/16-24 BSW (3/16 inch nominal diameter, 24 threads per inch), or 1/4-20 BSW[4] for smaller cameras and 3/8-16 BSW[5] for larger cameras and pan/tilt heads. In this application, the BSW and UNC thread profiles are similar enough that one can mount a modern camera on a legacy tripod and vice versa. The UNC threads are a 60-degree angle and flattened, whereas the BSW are a 55-degree angle and rounded crest. However, at least one English manufacturer uses No.1 B.A. (British Association) for its tripod mount thread.

When deciding for the brand, I went with German manufacturer Völkel which are producing industrial quality threading tools.

As there are lots and lots of different tool combinations to choose from, I'm putting up the exact item numbers you need to buy for anyone in the same situation like me. All tools are high quality made from HSS steel. You also should use universal cutting oil, just in case.

For 1/4 UNC:
Hand tap set, ≈ DIN 352, HSS-G, UNC 1/4 x 20 (item # VOE23314)

Round Dies, DIN 223 (DIN EN 22568), HSS-G, UNC 1/4 x 20 (item # VOE23414)

Die Stocks, Zinc die cast (mm) DIN 225 (DIN EN 22568) Size 20 x 7 (item # VOE15003)

For 3/8 UNC:
Hand tap set, ≈ DIN 352, HSS-G, UNC 3/8 x 16 (item # VOE23318)

Round Dies, DIN 223 (DIN EN 22568), HSS-G, UNC 3/8 x 16 (item # VOE23418)

Die Stocks, Zinc die cast (mm) DIN 225 (DIN EN 22568) Size 30 x 11 (item # VOE15005)

One for both tap sets:
Adjustable Tap Wrenches DIN 1814 Size 1 (item # VOE13010)

Thread repair sets:
Thread Repair Kits, UNC 1/4 - 1,5D (item # VOE04107)

Thread Repair Kits, UNC 3/8 - 1,5D (item # VOE04109)