Non standard taps - what are they ?

I've just bought a handful of second hand taps, based on a description and a picture. What attracted me is they were described as M7, which although relatively unusual in the wider world, finds widespread use in the old Citroen cars I dearly love.

Anyway, when they arrived and I cleaned them up, they are anything but M7.

As we know, there's M7 coarse, with a 1mm pitch and M7 fine, with a pitch of 0.75mm. These taps have a pitch of 1.1mm.

These are the markings:

Brand: Winter, with a thistle logo

7 M/M (I've measured the major diameter at 7mm)

1.1 (I've measured the pitch at 1.1mm)

Then there is a further engraving that says.....

Either L’H’Z or Z.H.L or just possibly Z.H.7 ?

Googling around suggests there is a German standard for a largely obsolete Löwenherz thread that has a pitch of 1.1 mm for a diameter of 7mm, so in the absence of a better idea, I assume that's what these are. The pitch angle for this thread is 53.13 degrees, but I've no way of checking this in my workshop. (**LINK**)

Does this spark any thoughts ? Anyone need them

Will this work ? link to other pictures: **LINK**

Edited By Andrew Cox 3 on 03/06/2020 17:17:20

I think the L'H'Z is indisputable and that your assessment is correct.

With regard to the thread angle, you might take a very close up shot, very square, and put into your album.

It can then be imported into a CAD program and lines overlaid to estimate thread angle (modern day poor man's optical comparator).

Time for a macro photograph.

Martin C

Now all you need is a 7mm x 1.1mm die and your could incorporate 'Lionheart' threads into future projects.

https://www.practicalmachinist.com/vb/antique-machinery-and-history/winter-brothers-tap-die-history-339153/

https://archive.org/details/WinterBrothersCoCatNo5/mode/2up

Apparently used in Germany for measurement machines and optical ! Now obsolete.

You might have a go at selling them on ebay, a German enthusiast might want them. There are 7mm threads used today on bicycles I seem to recall, but I doubt if the pitch is 1.1mm.

Early Lorch lathes used Lowenhauser threads I believe.

regards

Using a 1mm pitch and a 1.1mm pitch would enable a differential of 0.1mm per rev between two items on a single shaft. I can see how that would help with a measuring or optical system. It would be relatively easy to create the two different threads on a shaft without specific dies but easier to cut the internal 1.1mm pitch with a tap.

Martin C

Thanks all, and thanks specifically to DC31k for the link to the Winter Brothers catalogue; that confirms they were the manufacturer as they use the thistle logo.

Don't some modern brake bleed screws use M7?

Yes they do but with the standard 1mm pitch and the standard 60 degree ISO thread angle. The Lowenherz thread uses a 53 degree 8 minute thread angle along with the odd pitch. Details here.....

All is not lost. You can use one/some of them to make some dies, to match your taps. Then make your own bespoke/unique nuts and bolts.🙂

Or just print a section of the photo big on your printer and use a protractor.

Quite regular on motorbikes. Older Czech engines like MZ had them and there are many many Suzuki motorbikes right up to present day use M7 for the engine valve cover bolts.

We’re they expensive?

M7 is very common on Bugattis among other odd threads.

In my second life after teaching I repaired all sorts of metal antiques as well as building railway locomotives. The starting point was Mike, vernier, thread pitch gauges and Zeus chart and the bible ~ machinery handbook. I have found imperial diameters with metric , imperial and whatever US pitches they fancied.

0ba and m6 are same dia but different thread angles 47.5 and 60 degrees but will screw together. Not safe.

quite often the blacksmith would make an external thread from a suitable material, cut flutes, harden and from that make a die. Don't worry about the size as he made one to fit the other.

My 'bible' for threads is "Guide to World Screw Threads" by P.A Sidders Originally Published in England as "Machinery Screw Thread Book" it is now published by Industrial Press Inc.of New York (ISBN 0-89381-1092-9).

It confirms that one benefit of metrication is that it allows everyone to have their own standard. For example, there are French Automobile metric threads, both fine and coarse, as there are Japanese Automobile threads, again very fine, fine and coarse. Swiss Metric threads, instrument threads such as microscope objectives and nosepiece threads, camera threads (generally used in lens mounts the ubiquitous tripod thread in the camera base is 1/4" BSW! ) Then there are the Horological series, that is all before we get to the Eddison light bulb thread, the German bottle closure thread and not least the 'water tap rope thread' and the Sewing Machine Series threads. It also lists the Lowenherz thread series but interestingly it does not cover the Schaublin collet thread (a 5/45 buttress or more accurately a Sagengewinde or saw tooth form with a 1.66mm pitch!! that one caught me out a few years ago when I came to make a draw bar for my Aciera F3 mill - but that is a story for another time)

It lists the Lowenhertz thread series for 7mm as p = 1.1mm, Eff Dia = 6.175mm , Minor Dia = 5.35mm , Depth of thread = 0.825 mm & tapping drill = 5.5mm. Apparently the beauty of the Lowenhertz is the theoretical triangular thread depth is equal to the pitch. Thread angle, as stated previously is 53 degrees 8 mins