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Ammeter terminal thread

I picked up a non working CZ27 ammeter recently, cleaned up the internals and re-magnetised the magnet and it's a goer but it's missing the grub screws. Can someone please tell me what the thread is in these terminals?

Re: Ammeter terminal thread

Matty
1/4 BSF/BSC does it nicely on a spare CZ27 I have here. Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

0BA fits like a glove 😉

Re: Ammeter terminal thread

I did think 0BA which is the same 6mm X 25.4tpi as M6 (different thread angles though) , but it was a very loose fit in mine but a 1/4 BSF (6.35mm) screwed in nicely....But they can have a tendency to spread open because of the slot. Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

The two threads are quite different...The small difference in TPI (0BA..25.4 and BSF..26) will have no practical effect over a short thread of less than half an inch...

However, there is quite a difference in thread angle (0BA 47.5 degrees and BSF 55 degrees)

Also the outside diameter is quite different (0BA .236" and BSF .250) So a .012" difference...
They certainly shouldn't be regarded as interchangeable...

I would have thought 0BA would be the one based on my understanding that BA, also known as instrument thread, was employed on thing such as carbs, speedometers etc. which were classified as such...It may be though, that the BSF thread was used for the connection terminals...

I don't have one to hand to check unfortunately but I'd be interested in a definitive answer..Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

My money's still on 1/4 BSF/BSC. I just double checked and I can't screw either of my grub screws into an 0BA nut. But they do screw happily into 1/4 BSF. Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

Didn't we have the same discussion about the speedo mounting nuts?

Rob

email (option): robmiller11(a)yahoo.co.uk

Re: Ammeter terminal thread

We have discussed the speedo nuts Rob which is a different story really. Something to do with the speedo's being made under licence by the French company Jaeger and therefore the mounting studs are metric M6. I'd like to think that the hex would have been imperial or was a 10mm spanner required back then? But I guess your King Dick adjustable could be imperial or metric!! Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

The primary chain case screw thread comes to mind as well...:laughing: ...Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

Those are 3/16" I think Ian, Likewise the threads on the battery 'U' bolt. But 2BA seems the obvious option for the primary screws. Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

I had forgotten the metric outcome of the speedo thread thread and I couldn't find it using the search box, it just sounded familiar.

Rob

email (option): robmiller11(a)yahoo.co.uk

Re: Ammeter terminal thread

A helpful forum member had some of the 3/16" screws made (but of course I can't remember who) and I bought a few sets for my own consumption.. Certainly in the past they were a hard one to find and an alternative was required...I've used 2BA myself...Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

I agree with ron about 1/4 bsc but i will check this out.i have lots nos from this screws.

Re: Ammeter terminal thread

I have an ammeter on the bench and measured the threads. It is definitely 1/4" x 26 and not 0BA which is a smaller diameter. Now is it CEI (60 degrees) or BSF (55 degrees) my eyes are not good enough to see? I would bet on it being BSF.

Re: Ammeter terminal thread

Thanks Bruce...That pretty much rules out 0BA at least. We're more or less there!..Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

Oddly, the pre-war Lucas catalogues, in terms of ammeters refers to those with studs having a 2BA thread..But they give no sizes for the 'grub screw' variant.

Re: Ammeter terminal thread

Are the screws the same thread as the ones in the light switch terminal posts?...Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

I'll check tomorrow, but to my mind there's not enough room for a row of 1/4" screws? Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

I just check my nos grub screws by put it against a 1/4 bsc bolt and can say it fits great.

Re: Ammeter terminal thread

Cheers Roy and I just checked a headlamp switch, the grub screws are 2BA. Ron

email (option): ronpier@talk21.com

Re: Ammeter terminal thread

Thanks Ron....Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

Thanks for all the input folks.

Re: Ammeter terminal thread

Ian Wright, I had the chain case screws, I later found out that they are a standard screw, I was conned! The American AF equivalent to our 3/16 cycle is 10 32. Why they use 10 instead of 3/16 I do not know, perhaps someone on here may know.

Re: Ammeter terminal thread

Hi Random...It's a shame you were conned...but on the other hand I was happy to buy them off you and get conned as well ..:laughing: ...Did I also get the gearbox inspection plate screws from you?....Ian:stuck_out_tongue_winking_eye:

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

Ian, very possibly. I bought 6 of your wheel bolts and a gear indicator plate from you at Stafford a few years ago.The inspection bolts are the the same as the B series rev counter gearbox bolts without the lock wire holes and just a bit longer.
Random...

Re: Ammeter terminal thread

How are these ammeters held into the headlight panel? Is it with a wire clip like the switch as unlike the reproductions it has no mounting posts?

Re: Ammeter terminal thread

Either the bezel or on some a collar around the base have little tabs that you fold up after it is fitted.

Re: Ammeter terminal thread

The bezel has protruding brass 'tags' (4) around its lower edge which are bent outwards behind the switch plate after the ammeter has been inserted into the hole...The ammeter also sits on a very thin 'O' ring which is placed under the bezel before fitment into the switch plate...Ian

email (option): ian@wright52.plus.com

Re: Ammeter terminal thread

ah ha, thank you gentlemen.

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