Lens mounting flanges & retaining rings - thread sizes

[Ron (Netherlands)]

At the LF forum with another member, I started a topic about how to measure the inside thread of vintage lens mounting flanges. The idea is to publish an inventory of members' piles of unused (mostly vintage) mounting flanges and retaining rings in order for other members to be able to find a matching ring which is missing on one or more of their vintage lenses; after a found match one might trade or exchange flanges/rings.

Because fellow members of PHOTRIO might also be interested, I'll start a comparable thread on the topic here. The topic may also extent to get an inventory on vintage lens threads finally resulting in a database.

For the ones who are not familiar with measuring threads: they are measured with a so-called thread gauge (cost are only a few dollars):

Such a gauge in combination with your (digital) calipers will help you find almost all the pitches and sizes of your lenses and mounting flanges:

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[Ron (Netherlands)]

Next I'll try to enumerate what I've found a practical means of measuring and presenting the size of the lens/shutter/flange. Their seem to be 3 categories of threads used on vintage lenses and their mounting flanges: Imperial, US and Metric.

Imperial (Whitworth) Thread sizes could be presented as follows:
Specifications mounting ring:
1. material: brass
2. OD (outside diameter): 2,420"
3. ID (inside diameter): 1.734"
4. TPI: 36
5. 3 screwholes
6. visible threads (groves): 6

However for our means/listing we only need the info mentioned under 3 and 4. After a match on these two data, one can always asked the owner of the flange to provide the other data.
In short the above ring could be described as 1.734-36, which means the ring has a diameter of 1.734 inch and there are 36 threads per inch. It appears that this ring matches the following vintage lens: Perken, Son & Rayment Portable Symetrical 5x7 'Optimus'

Metric Thread
The description for a Metric thread is a little different, since it counts the number of rotations to lift the ring one thread to the next. For example: 40,00mm-M0.9, which means that the flange has an inside diameter of 40 mm and has a metric pitch of M0.9. It happens that this retaining ring matches a Compur #2 shutter which can hold a Tessar f4.5 150mm lens.

US Thread was standardized in two ways: normal/coarse tread denominated as UNC and US fine thread denominated as UNF. They are presented in inch, but have a pitch angle and form that differs from the Whitworth thread: US have a 60 dgr angle and truncated crests whereas Whithworth has rounded crests at a 55 dgr angle.
For our means it would be best to describe the thread as done with the Imperial, and if we find a truncated crest, to mention it is UNC/UNF. So e.g. 2.500-30 UNC is the size of a flange which would fit a Ilex #4 shutter.

 

[Ron (Netherlands)]

If you find it practical and useful please let us know in this thread the sizes of your spare mounting flanges and retaining rings.
I'll put in my own list as well.