Pre-war Italian thread ?

[Tim StevensParticipant @timstevens64731]

I am working on a pre-war Marelli Magneto, and it has several screws 5.5mm diameter x 0.9mm pitch. My references cover UK, French, German and SI metric and I cannot find a match. Some of the screws have been attacked with screwdrivers which did not fit, and the heads are butchered.

Can you help with exact identity, or replacements (about 20mm or longer, domed countersunk heads) or even tap & die? – thanks

And happy Valentines Day to you all.

Tim Stevens
Welsh Marches – UK

[David JuppParticipant @davidjupp51506]

Could it possibly be 1BA?  Without knowing the history, it’s a bit of a guess – but the design could have been licensed in from elsewhere.  Hence may not have been an Italian thread at all.

[noel shelleyParticipant @noelshelley55608]

5.5 x .9 is a metric size and taps an dies are available from Tracy tools, or it may be 1 BA at 5.3 x.9. Good luck. Noel.

[Howard LewisParticipant @howardlewis46836]

1 BA is 5.3 mm dia and 0.9 mm pitch, as already intimated.

Being Magnetti Marelli, and so electrical, quite a possibility, IMO

Howard.

[JasonBModerator @jasonb]

5.5 Loew is 5.5 x 0.9

Close to 7/32″ x 28 BSF or #12-28 UN

 

[NimbleParticipant @nimble]

Hi Tim,

Perhaps you could contact “The Magneto Guys”  https://www.themagnetoguys.co.uk/  .

They seem to be pretty good about giving out information.

Good luck.

Nimble Neil.

[Tim StevensParticipant @timstevens64731]

It could indeed be 1BA, except that the measured od of the screws is a bit larger. So, properly speaking, 1BA is what I need, as the profile of the thread is unique with angles of 47.5 degrees between the flanks. So, who makes or sells 1BA screws – preferably in stainless steel?

Thanks David – I never thought to check if BA was used, as it is only found (in my experience) in models, and old electrical plugs etc.

Tim Stevens

[bernard towersParticipant @bernardtowers37738]

If you only need a few it would be simpler to make them yourself.

[noel shelleyParticipant @noelshelley55608]

In answer to who makes/sells 1 BA try EKP Supplies. Good Luck. Noel.

[Stuart Smith 5Participant @stuartsmith5]

My friend is restoring an old Italian motorbike and was struggling to find some M7 bolts.

After searching everywhere, he eventually obtained some from a local shop in Preston. (Allthread fasteners).

This is the link to their website:

https://www.atfltd.com/

Worth asking them.

 

Stuart

[CirclipParticipant @circlip]

Rear brake linkage to master cylinder is an M7 thread on me Guzzi Le Mans, ended up thread cutting it meself from 304.

Regards  Ian.

[Charles LamontParticipant @charleslamont71117]

M7?  Every day is a school day.

[noel shelleyParticipant @noelshelley55608]

M7 x 1 is a standard metric thread and commonly available, but not a preferred size !

If the screw is a big 1 BA ( oversize ) then UNLESS your sure it is 47.5* thread angle it will be 5.5 X .9, a normal metric thread. Wear and machining tolerances may well allow both to fit. Noel.

[Martin ConnellyParticipant @martinconnelly55370]

Personally I would just get out my metric thread gauges and try the 0.9 gauge against a screw with a light behind. This will quickly show if it is a BA thread because there will be lots of light showing if it is. If you intend to do work on equipment with unknown threads then thread gauges seem to me to be a good investment.

Martin C

[Speedy Builder5Participant @speedybuilder5]

M7 – Citroen 2cv all over the place, engine, chassis etc.

Bob

[Speedy Builder5Participant @speedybuilder5]

1Ba, if you have a model steam loco club nearby, Ba are used extensively on the older models and plans – not stainless though (unless you are very lucky). Mind you, domed CSK are a bit rare!

Bob

[bernard towersParticipant @bernardtowers37738]

As I said earlier you could have made them by now.

[bernard towers]

On bernard towers Said:

As I said earlier you could have made them by now.

Tim doesn’t have taps or dies and we don’t even know what the thread is yet. Five possibles suggested and it could be continental or even non-standard. I’d order a few 1BA and M5.5×0.9 in hope one will fit.

Dave

 

 

 

[Martin ConnellyParticipant @martinconnelly55370]

I had to make a couple of screws for a friend who restores large music boxes. Many were made in Italy, Switzerland and that general area. The thread on those screws was a Löwenherz thread form and one of the listed sizes is Ø5.5×0.9 pitch. I think a quality photo zoomed in from a distance against a plain background is needed for the angle of the thread to be measured, much like a shadowgraph. Just guessing when there are so many possibilities is not going to achieve much. There is a possibility of forcing an incorrect thread form into the hole and it putting excessive unusual strain on a hard to replace part.

Martin C

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