Which thread is recommended, please?

Hi, going to start building brass skeleton clocks from scratch. Which is the best thread for screws, nuts and bolts, and why? Thanks in Ada Vance. Mark

Hi Mark,

Will you be aiming for authenticity or convenience?

Will you be screw-cutting in the lathe or using standard dies?

Designed prior to 1972, John Stevens' skeleton clock uses BA.

There are other members far better qualified who may come along shortly.

Good luck,

Sam

My first few clocks built in the 90s used BA threads but I now only use standard metric. There are a vareity of pitches for each size and fateners are plentiful or easy to make your own. Metric sizes also integrate better with metric stock materials and metric dimensions. Can't see any advantage in using BA sizes any more.

Metric now.

It is ‘sad but true’ that the standardisation and mass-production of ‘Metric’ threads has made their use a no-brainer.

The BA series, and the Swiss Thury series which inspired it, were both developed by Scientists, and are scientifically elegant … By contrast, the Metric series is much simplified, for the sake of expediency.

MichaelG.

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Edit: __ This is a convenient entrance to the rabbit-hole :

https://www.sizes.com/tools/thread_thury.htm

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Edited By Michael Gilligan on 01/10/2023 07:13:02

Looking at the Chart Michael links to there is really very little difference between what it shows for the thread sizes you are likely to find on a clock say M1.6 to M6 all pitches if you pro rata them to what is shown they are within 0.1mm mostly 0.05mm

Add to that as Foggy say you can get several pitches if you need something finer than the standard coarse pitch and I see little point in using BA, only real reason may be that 2, 5 and 7 work well on fractional imperial stock but as metric is easy to find these days not an issue.

Tooling is also more plentful in metric with choices in types of tap etc

I restore torsion clocks and mostly they use BA threads from about 1915 to mid 50’s when they are mostly metric , before approximately 1915 they are Thury or lorence ( think I spelt it correct) but as every thing there are exceptions, I can’t see using metric as a problem modern clocks modern threads.

Dell

i did get name wrong it’s Lowenherz

Edited By Dell on 01/10/2023 08:25:31

I did get the thread name wrong

**LINK**

I vote metric too.

BA might be more aesthetically pleasing because the heads and nuts are a little smaller, but apart from that go for cheapness and high-availability. In the most of the world that means metric.

Dave

Even then you can get smaller hex metric fixings which I use all the time or just make your own if commercial is not to your liking

Many of the commercial metric hexagon-headed screws have rather ugly embossed numbers on them, but you can face them for appearance, and really, I don't think there is a noticeable aesthetic difference between many ISO-M and near-equivalent BA dimensions, for most applications.

BA is metric anyway, just specified in inches, though of its own angle, diameters and pitches.

Size-smaller metric screw-heads may be available though the bureaucratic rather than geometrical ISO-Metric sequence, with no numerical relationships, hinders that by large spanner increments with random jumps in the series. Often acceptable in large-scale model-engineering, and workshop duty, but not ideal for fine-scale modelling and horological work.

I have not seen size-smaller metric nuts but where these really matter, are not difficult to make if the hexagon stock is available. I don't know if the ISO-Metric Fine thread series has corresponding hexagon proportions.

Anyway, don't clock screws normally have slotted, round heads? I don't recall seeing hexagon-headed screws on clocks I have examined in exhibitions. Nor do they have many nuts.

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The Thury thread others cite, was developed for clock and instrument making.

Edited By Nigel Graham 2 on 02/10/2023 11:01:39